Where can I find a dictionary which contains an article on the word lavra? What does the word mean and is it really used?
It's not an English word, except as a borrowing from Greek. It means a particular sort of religious community, primarily in the Orthodox Christian church(es). It's not used except by people who are talking about religious communities, because it's not a common phenomenon in English-speaking countries.
You'll find it in an encyclopedia, or a dictionary of religion, not a general dictionary.