Five M-words
The so-called Five M-words are Matsya (approximate meaning: fish), mamsa (flesh), madya (fermented grain, i.e. wine), mudra (in this context, frumentum) and maithuna (fornication).
The practices related to the Five M-words (sometimes referred to as pancamakara) have remained contraversial since they were first described in scandalised tones by Western orientalists. Western New Agers have 'read' the Five Ms as a purely erotic, blissful communion, whilst those who deny that Tantra had anything to do with sexual practices insist that the Five M-words are to be understood purely metaphorically.
Wendy Doniger, in a recent review of David Gordon White's Kiss of the Yogini notes that the Five M-words are probably historically related to the panchagavya - the "five products of the cow" (ghee, milk, yoghurt, urine & faeces) all of which are employed to purify those who have temporarily become polluted:
From The Laws of Manu.XI.166 : "(To swallow) the five products of the cow pankagavya) is the atonement for stealing eatables of various kinds, a vehicle, a bed, a seat, flowers, roots, or fruit."
Some early Dharmashastra texts note that the use of the panchagavya was forbidden to women and the lower castes.
Doniger also notes that the Five M-words were also related to earlier pentads of substances - for example the Five Nectars which are sometimes exoterically given as: honey, sugar, curds, milk, ghee and water, - all of which are offered to the gods - but in the Kaula context were semen, urine, faeces, menstrual blood and marrow - a typically Kaula reversal of Brahmanic categories of purity:
"In Kaula Agama, the five pure and eternal substances are ash, wife's nectar, semen, menstrual blood and ghee mixed together. In occasional rites and in acts of Kama Siddhi, the great discharge is without doubt and most certainly what one should do in Kaula Agama. One should always consume the physical blood and semen. Dearest One, this is the oblation of the Yoginis and the Siddhas".
(From the Kaula Jnana Nirnaya attributed to Matsyendranath)
According to David Gordon White, writing in Kiss of the Yogini, the use of the term mudra within the context of the Five M-words refers not only to the infamous vajroli mudra practice, but also, the vulva of the male practitioner's consort - and by extension, her sexual emissions. He also argues that the term maithuna within the Kaula context refers not merely to intercourse itself, but "[that] which is derived from intercourse, i.e. its fluid products.
In later (post-Abhinavagupta) forms of Tantra, the meanings of Five M-words shifted away from bodily substances to become 'codes' for ritual substances or states of consciousness.