In plain words
The word 'svāhā' is not merely a technical term indicating the fire-offering; it is meaningful speech.
'Chandayati' [the root]: gladdening, and 'cādana' means becoming strong, becoming endowed with vital power, and covering/sheltering. Because of possessing just such a strength of Dharma, the Vedas bear the name 'chandas' [metres]. The Taittirīya Śruti has expounded at great length those persons, endowed with great power, who thus shelter the Veda. Such a rite is not for a single individual alone but bestows a delight that transcends the ordinary world. Names such as 'yajñāṅgaḥ' [whose limb is sacrifice], 'yajñavāhanaḥ' [whose vehicle is sacrifice], 'vṛṣarathaḥ' [whose chariot is the bull] have been applied to the Supreme Lord in the Śruti and Smṛtis. Hiraṇyagarbha is golden, made of the Vedic metres. 'Golden' here means Garutmān, [that is,] Garuḍa — he who accepted the embodiment of the metres as his own vehicle.
'Vṛṣa' [bull] means the very form of Dharma; taking Dharma itself as his vehicle is what is meant. In Viṣṇu's temples, Garuḍa, and in Śiva's temples, the bull [Nandī], are placed as pillar-images in front of the gateways — their standing there carries this very inner meaning.
'Chādana' [covering] means the protection of the tree of saṃsāra. For those who move about in their actions desiring the fruit [of those actions], [the chandas] veil the ultimate truth [for a time], make them steadfast in Dharma, and so keep protecting the tree of saṃsāra. As for those devoted to [ritual] action, [the chandas] shelter them from a 'death by [excessive] Dharma'; and they veil and so protect the knowers from a 'death by saṃsāra'. Those that thus protect are called, precisely, 'chandas', and those very chandas are called 'Vedas' — so it has been said. 'From sheltering [beings], they are chandas' — because able to protect from death, the chandas are the very cause of well-being [śarma]. The sacrifice, having departed from the gods and taken the form of a black antelope, was roaming about; the gods followed closely behind and were finally able to seize its hide. The very body of the sacrifice is the black-antelope skin. The white, black and reddish-brown colours in it are the forms of the Ṛgveda, the Yajurveda and the Sāmaveda. Therefore it was determined that the black-antelope skin is the very embodiment of the Ṛg-, Yajur- and Sāmaveda. This they called the embodiment of the triple sacred knowledge. Since the action enjoined by the triple [Veda] is accomplished [through it], the sacrifice too is [held to be] the very embodiment of the triple [Veda].