well, you can name files whatever you want aslong as the final extension is php (and others with some server adjustment). so, without seeing the code, they could be anything.
api, in programming terms stands for 'application programming interface'. so i would say these files are some sort of wrapper. making it easier to use a specific set of tools.
eg: i wrap all my database connection and query functions into one class. this 'class' could be considered somewhat of an api for a mysql database.
by the way, i name my classes like : mysql.class.php
of course, im only new to php myself, so these file types may have more too them. but i havent seen it.
hope this helps.
