Q. What is the meaning and source for some congregations and people keeping a fast day or reciting Selichos during ‘Bahav.’ firstly, what does ‘Bahav’ mean?
A. There are several minor customary fast days, that are not universally observed, and some include: "Bahav," literally an acronym for "Monday, Thursday, Monday" and are the Monday, Thursday, and the following Monday in the months Cheshvan and Iyar, after the end of Pesach and Sukos.
Rabbi A. Bartfeld as revised by, Horav Dovid Pam, Horav Aharon Miller, Horav Chanoch Ehrentreu and Horav Kalman Ochs Shlit'a