In plain words
is a name. For that reason, the fruit-renouncing actions performed for the sake of attaining Brahman have come to be called both 'brahma-yajña' and 'ṛṣi-yajña'. All pure, auspicious, sattvic, selfless actions are themselves yajñas.
In such fruit-renouncing actions, an offering is repeatedly made while saying 'svāhā' again and again. Let us examine the meanings of the words belonging to the tradition of this word 'svāhā'. In ritual formulas such as 'To Keśava, svāhā; to Prāṇa, svāhā; to Indra, svāhā', the word 'svāhā' is commonly given the meaning 'may the oblation become well-offered' — that is the sense they give it.
What is meant by 'well-offered'? 'May the sacrificial substances released into the fire be consumed! May they be assimilated!' — that is the meaning. Here a doubt may arise. All substances put into fire quite naturally get consumed and assimilated, do they not! Then what special effect does the utterance of svāhā bring about? 'Svāhuti' does not mean merely burning objects and digesting them — that alone is not the [full] purport of the Śruti. The becoming-burnt is only what is directly perceptible; the Vedic view is different.
In the poem Kumārasambhava, Kālidāsa, describing the Himālaya, called it 'devatātmā'. That is to say, each thing has two bodies — a divine body and a physical body — and this is sanctioned by the Śruti. The divine body is beyond the senses; the physical body is joined with the [physical] senses and organs. In the divine body, fire becomes the vital fire, prāṇāgni; and within that, the oblation becomes the true havis. The Śruti explains the true nature of the oblation thus: 'attā' [the eater] and 'adyam' [the eaten] — that is, the enjoyer and this world which is in the form of the enjoyed — when the two become one, combining both together, it is called 'attā' alone, that is, the enjoyer alone; that alone is the usage. Who is that enjoyer? It is fire itself. In its divine aspect, it is Āditya; in its inner aspect, it is prāṇa. Such food-oblations and the like, placed with the [sacred] mantra in that vital fire, are named 'āhitayaḥ'.