They're also grouped by position.
From the help page:
Free-Agent Type - This indicates the type of free-agent that caused this pick to change hands. Type A players are those who rank in the top 20% at their position group in the big leagues (C, 1B/OF/DH, 2B/3B/SS, SP and RP). Type B players rank between 20% and 40% at their position groups in the big leagues.