How to identify a transaction table?

Question

i have database that has master tables prefixed with `mt_` and transactions tables prefixed with `tr_` . But when i go through the database i started to wonder what is the actual definition of a transaction table and master table. To my understanding transaction table should have a composite primary key (primary key made from two or many PKs of other tables). But when i looked at the transaction tables in database, there are tables that have the composite key as mentioned previously also it has tables tagged as tr_ but have only one key tagged as PK and they also have PK keys that belongs to other tables but they weren't even tagged as FK...

So could any one here explain the difference between a master table and a transaction table and how to identify them in DB?