जातेरस्त्रीविषयादयोपधात्

The feminine affix ङीष् comes after a word denoting a जाति or species when it does not express in its original meaning a feminine and which moreover has not the letter य् for its penultimate.
The word जाति was defined under Sutra 1.2.52. Thus कुक्कुटी 'a hen'; सूकरी 'a she-hog', ब्राह्मणी 'Brahmani'; वृषली 'a woman of the Sudra caste', नाडायनी 'a woman of Nadayana class', चारायणी 'a Charayani', कटी 'a woman of Brahmans who read the Katha', बह्वृची 'a woman of the class of Brahmans who read the Rig Veda'.

Why do we say "expressive of a jati"? Observe मुण्डा 'shaven' ( where the word expresses not a jati but a quality). Why do we say "not invariably feminine"? Witness मक्षिका 'a fly' (supposed to breed without a male). Why do we say "not having the letter य् for its penultimate?" Witness क्षत्रिया 'a female of the Kshatriya class'.

Vart:- In excluding words that have the letter य् as penultimate, there is not involved the exclusion of the following words which have a penultimate य्) viz, गवय 'the Bos Gaveans', हय 'horse', मुकय 'a sort of animal', मत्स्य 'a fish', and मनुष्य 'a man'. Thus गवयी, हयी, मनुषी, (6.4.150 हलस्तद्धितस्य 'there is elision of the य् of a taddhita affix coming after a consonant when long ई follows') मत्सी ॥ The य् of matsya is elided by the vartika 'मत्स्यस्य ङ्याम्' ॥ See also 6.4.149. All these words are also included in the class गौरादि 4.1.41 and would have taken ङीष् independently of this vartika.

Another definition of jati is:-

प्रादुर्भावविनाशाभ्यां सत्यस्य युगपद्गुणैः ।
असर्वलिंगां बह्वर्यो तां जातिं कवयो विदुः ॥ (See translation under 1.2.52)