I've seen too many people using 'cat' as a short cut for 'category'

About the naming convention ... I think it's used that way so you don't get confused or type too much when selecting from multiple tables ... i.e: you don't have to say posts.post_id ... otherwise if you're selecting from 2 tables that have the same field name you'll have to do something like posts.id and if you want to use it somewhere you'll have to provide a temporary name using 'As `fields`'

At least that's what I remember from my readings.