Panchamahabhutas (also known as pancha-bhutas OR mahabhutas) is the samskrit term made up of 3 parts. Pancha means 5, maha means big and bhutas means the existing elements. Thus, the term panchamahabhutas indicates 5 basic elements existing in the universe. These are considered as the basis of creation of matter and space in the universe. Human being a part of the universe is also made up of these 5 basic elements. These 5 basic elements have specific attributes, owing to which how they would act or affect the others is decided. They co-exist in all the materials or matters in this universe in varied proportion. One or 2 elements might be present in dominance than others in different matters. Dominance of mahabhutas decide the final quality or nature and behavior of that matter in this world.
The 5 elements
Kha/ Aakasha, Vayu, Teja/ Agni, Jalam/ aapa, Bhu / Prthvi/ kshiti are the 5 basic elements or panchamahabhutas existing in the universe. Each of these 5 mahabhutas have one unique quality. This quality is specific to that mahabhuta and called as guna (quality) of that mahabhuta.
महाभूतानि खं वायुरग्निरापः क्षितिस्तथा| शब्दः स्पर्शश्च रूपं च रसो गन्धश्च तद्गुणाः||२७|| Cha Sha 1.27
Meaning: Kha (ether), Vayu (Air), Agni (fire), Aapa (Water), Kshiti (Earth) are called mahabhutas. Shabdam (sound), Sparsham (touch), Rupam (vision), Rasa (taste) and gandha (smell) are the gunas (unique qualities) of these mahabhutas respectively.
॥ शब्दगुणकमाकाशम्। तच्चैकं विभु नित्यञ्च॥५॥
The word Akasha literally means ‘a free or open space’ or ‘the ether’, ‘sky’ or ‘atmosphere’.
॥ रूपरहितः स्पर्शवान् वायुः। स द्विविधः नित्यः अनित्यश्च। नित्यः परमाणुरूपः। अनित्यः कार्यरूपः। पुनः त्रिविधः शरीरेन्द्रियविषयभेदात्। शरीरं वायुलोके। इन्द्रियं स्पर्शग्राहकंत्वक् सर्वशरीरवर्ति। विषयो वृक्षादिकम्पनहेतुः। शरीरान्तः सञ्चारी वायुः प्राणः। स च एकोऽपि उपाधिभेदात् प्राणापानादिसंज्ञां लभते॥४॥
The word ‘vayu’ literally means ‘wind’ or ‘air’ or ‘vital air’.
॥ उष्णस्पर्शवत् तेजः। तच्च द्विविधं, नित्यमनित्यं च। नित्यं परमाणुरूपम्। अनित्यं कार्यरूपम्। पुनः त्रिविधं शरीरेन्द्रियविषयभेदात्। शरीरमादित्यलोके प्रसिद्धम्। इन्द्रियं रूपग्राहकं चक्षुः कृष्णताराग्रवर्ति। विषयः चतुर्विधः, भौम-दिव्य-औदर्य-आकरजभेदात्। भौमं वह्न्यादिकम्। अभिन्धनं दिव्यं विद्युदादि। भुक्तस्य परिणामहेतुरौदर्यम्। आकरजं सुवर्णादि॥३॥
‘Agni’ literally means fire. In Ayurveda biology, agni denotes all factors responsible for digestion and metabolism/transformation. (Code:SAT-B.488) It is the heat (ushma) generated from pitta dosha in the body. Therefore, all functions of agni are similar to pitta dosha.
॥ शीतस्पर्शवत्यः आपः। ता द्विविधाः, नित्या अनित्याश्च। नित्याः परमाणुरूपाः। अनित्याः कार्यरूपाः। पुनस्त्रिविधाः शरीरेन्द्रियविषयभेदात्। शरीरं वरुणलोके। इन्द्रियं रसग्राहकं रसनं जिह्वाग्रवर्ति। विषयः सरित्समुद्रादिः॥२॥
The word ‘jala’ literally means ‘water’ or ‘any fluid’. It is also known as ‘ap mahabhuta’. The word ‘ap’ also means ‘water’.That which have the sensations of vision (rupa), taste(rasa), touch (sparsha), sliminess (snigdha) and is in the form of liquid (drava) is called ‘ap’ [Vaisheshika sutra]. It is cold on touch [Tarkasangraha].
Tarkasamgraha- ॥ तत्र गन्धवती पृथिवी। सा द्विविधा, नित्याऽनित्या च। नित्या परमाणुरूपा। अनित्या कार्यरूपा। पुनस्त्रिविधा शरीरेन्द्रियविषयभेदात्। शरीरमस्मदादीनाम्। इन्द्रियं गन्धग्राहकं घ्राणम्। तच्च नासाग्रवर्ति। विषयो मृत्पाषाणादिः॥९॥ 
(TBE)The word ‘Prithvi’ literally means ‘the earth’. It also represents the earth in its elemental form. Prithvi has been derived from the word ‘pruthu’, which means ‘possessing sthula guna (property of bulkiness or thickness)’. Prath also means pervasive, which spreads. Another meaning is particles. Prithvi is the one which is composed of several particles. That which have gandha (smell), rasa (taste), rupa (vision) and sparsha (touch) is called prithvi.
Place of panchamahabhutas in the cosmic evolution (Srshti utpatti)
The Srshti (universe) is evolved from unmanifest (avyakta) through cosmic inltelligence (mahat) and ego (ahamkara). Then the panchatanmatra are evolved from rajas dominant taijas and tamas dominant bhutadi ahamkara. Panchatanmatras are the subtle forms of panchamahabhuta from which the panchamahabhutas develop in the later stage. Ayurveda has accepted this Srshti utpatti siddhanta propounded by Samkhya darshana.
As per the Srshti utpatti siddhanta of darshana shastras accepted by Ayurveda, mahabhutas are evolved sequentially from akasha to prthvi. In this process the quality of that mahabhuta which gives rise to the other, is transmitted in the newly evolved mahabhuta. Since Akasha mahabhuta is the first to evolve in sequence, its unique property becomes part of all 4 mahabhutas evolving after it. Same applies to all the other mahabhutas after akasha. This transmission of qualities is called as Bhutanupravesham explained in Charaka Samhita as below,
Bhutantara praveshakrit gunas (भूतान्तरप्रवेशकृतं गुण)
तेषामेकगुणः पूर्वो गुणवृद्धिः परे परे| पूर्वः पूर्वगुणश्चैव क्रमशो गुणिषु स्मृतः||२८|| Cha sha 1.28
Meaning: The order of mahabhutas mentioned above is important because, starting with akasha, the number of attributes per mahabhuta increases in the above order. This increase in number of attributes is cumulative, i.e., the attribute of the preceding mahabhutas is added to the succeeding one. This process of gunantara vriddhi in mahabhutas is also known as bhutanipravesha. (charakasamhitaonline.com)
Basic properties that can be perceived by human through touch
Each mahabhuta possesses specific qualities. This gives rise to a characteristic feature in each mahabhuta. This characteristic feature helps us to identify the presence or absence of that particular mahabhuta. It can be assessed through touch by assess.
खरद्रवचलोष्णत्वं भूजलानिलतेजसाम्| आकाशस्याप्रतीघातो दृष्टं लिङ्गं यथाक्रमम्||२९|| लक्षणं सर्वमेवैतत् स्पर्शनेन्द्रियगोचरम्| स्पर्शनेन्द्रियविज्ञेयः स्पर्शो हि सविपर्ययः||३०|| Cha sha 1.29-30
Meaning: Prithvi, jala, agni/tejas, vayu and akasha are characterized by kharatva (roughness), dravatva (liquidity), ushnatva (heat), chalatva (mobility) and apratighatatva (unobstructibility) respectively. All these attributes are perceptible by the tactile sense organ. Touch, together with its absence, is perceived by the tactile sense organ.
Fundamental composition of any element in this nature can be assessed on the basis of these peculiar characteristics. The same is applicable to human body as well. While diagnosing and treating the imbalances in body, the increase or decrease in these features is considered crucial parameter to understand dosha – dhatu disequilibrium. This is the clinical application of the panchamahabhuta siddhanta and is considered as one of the fundamental siddhanta in Ayurveda.
Mahabhutas and trigunas Association
Each mahabhuta has a fixed association with the trigunas. This association is considered important while understanding functions of various elements in the universe and human systems as well. This association is described by Acharya Sushruta as below,
तत्र सत्त्वबहुलमाकाशं, रजोबहुलो वायुः, सत्त्वरजोबहुलोऽग्निः, सत्त्वतमोबहुला आपः, तमोबहुला पृथिवीति ||२०|| Su Sha 1.20
Meaning: Akasha is Sattva dominant, Vayu is rajas dominant, Agni mahabhuta is Sattva and rajas dominant, Apa is Sattva and tamas dominant whereas Prthvi mahabhuta is tamas dominant.
Application of panchamahabhuta siddhanta in Ayurveda
भूतेभ्यो हि परं यस्मान्नास्ति चिन्ता चिकित्सिते ||१३||
यतोऽभिहितं- “तत्सम्भवद्रव्यसमूहो भूतादिरुक्तः” (सू.१); भौतिकानि चेन्द्रियाण्यायुर्वेदे वर्ण्यन्ते, तथेन्द्रियार्थाः ||१४|| Su Sha 1. 13-14
Panchamahabhutas association with humans
The purusha holistic human being is formed by unification of panchamahabhuta and consciousness (chetana). [Cha.Sa.Sharira Sthana 1/16]
Panchamahabhutas and food
Deha means shariram. Sharira (शरीरम्) i.e. physical body of living beings is made of body tissues called as dhatus. All these dhatus are in turn made of of 5 mahabhutas (पञ्चमहाभूतानि) and therefore the body is said to be made of 5 mahabhutas (panchabhautika deha - body made up of 5 elements). On the basis of doctrine of samanya vishesha siddhanta (सामान्य विशेष सिद्धांतः) body made up of 5 mahabhutas can be nourished and grown only with the help of something that is also made up of 5 mahabhutas.
पञ्चभूतात्मके देहे ह्याहारः पाञ्चभौतिकः | विपक्वः पञ्चधा सम्यग्गुणान् स्वानभिवर्धयेत् ॥ (Sush. Samh. .46.526)
pañcabhūtātmake dehe hyāhāraḥ pāñcabhautikaḥ | vipakvaḥ pañcadhā samyagguṇān svānabhivardhayet ॥ (Sush. Samh. .46.526)
Thus Ahara (food articles) is looked upon as the source of these 5 mahabhutas which can later form dhatus/body tissues and cause development of body. It is stated that the 5 mahabhutas in body are replenished and grown by 5 mahabhutas in food after process by separate agni (अग्निः) for each mahabhuta present in the food itself. During the processing of food by agni of mahabhutas called as bhautikagni (भौतिकाग्निः), transformation of external mahabhuta into body type mahabhuta takes place. The transformed mahabhutas then finds the place in dhatu (धातवः) and become a part of shariram. 
- Tarkasamgraha By Annambhatta, Dravyalakshana prakaranam