An Aticāra (partial transgression) of the fourth vow of the lay follower (viz., abstinence from sexual activity with a person other than one's spouse);
indulgence in unnatural sexual intercourse, i.e., sexual enjoyment through bodily organs other than genitals.
(TaBhā 7.23 Vṛ)
hastakarmādīcchā.
aṅgaprajananaṃ yoniśca tato'nyatra krīḍā anaṅgakrīḍā.
anekavidhaprajananavikāreṇa jaghanādanyatra cāṅge ratirityarthaḥ.
(TaVā 7.28.31)
anaṃgāni maithunakartnāpckṣayā kucakakṣoruvadanādīni teṣu krīḍanamanaṃgakrīḍā.
(Upā 1.35 Vṛ p.13)