This is the 10351st most frequent Russian word.
бывшей
The Russian word "бывшей" means "former" or "ex-" in English.
Here, 'бывшей' is the feminine instrumental singular form of the adjective 'бывший' (former), modifying 'коллегой' (colleague), indicating a person who was a colleague in the past.
Она пошла на встречу со своей бывшей коллегой.
She went to meet with her former colleague.
In this sentence, 'бывшей' is the feminine dative singular form of the adjective, describing 'жене' (wife), indicating that the person was his wife previously.
Эта квартира принадлежит его бывшей жене.
This apartment belongs to his ex-wife.
Here, 'бывшей' is the feminine prepositional singular form of the adjective, qualifying 'школе' (school), denoting a place where the person previously studied or attended.