It is a latin phrase often used in English to me For this or about this referring to a loosely put together group. An Adhoc committee was assembled to solve the problem. Meaning the group was casually put together. It is seen in newspapers, but not in normal conversation

I would use it in conversation. I would say that I did something in an ad hoc way, meaning I didn't have a plan, but just made it up as I went along. I work in the UK civil service, and maybe it's the culture of our work but people quite often use Latin phrases in speech in the office. Other examples of Latin I've heard used in conversation include: Mea culpa (it's my fault) or Ad nauseam which is usually repeating something ad nauseam (that is, until you're totally sick of it!)