We did have tag definitions at one point but with the changes that are being applied to fakku they are temporarily unavailable to see (sorry about that). What I would do is just google the names you don't know, there should be a definition such as on urban dictionary. The images for the tags should also give you an idea as to what the focus on the genre is such as pettanko meaning "small breasts" or "shimapan" showing stripped undies, etc.