Recently, I spoke to a neighbor who had a 20 year old daughter. I asked the mother if she was dating anyone and she responded that she was "in the parsha". This is a new term to me. I assume the term means that she is shidduch "eligible" or does it mean something else? When did this term originate? Is this becomoing a universally accepted term these days? I must be "out of it" (the terminology AND the parsha, that is...)
I hear it exclusively from the Litvish/Yeshivish type crowd, although that doesn't mean it doesn't transfer out over time. It means actively seeking shidduch opportunities - i.e. talking to Shadchanim, going out on dates.
It is probably not earlier than late 20th century, certainly not in common usage, as I remember when I would hear it said differently from people connected to those communities.
I think that the idiom is based on the idea of a person being "betoras hadavar" when something applies to them. Consider a person being "Betoras chasuna" as an example. I think that there are references of that type when a person is chayav a particular mitzvah. Perhaps like a kohen is "in the parsha of duchening".