Full-scout: Remnant of previous front-office system, having Scouting OFF will give you fully accurate information of a players ratings.
Mis-scout: Sometimes, players just don't display accurate scouting when attempting to scout and their full scouted numbers are different than what you may have scouted them as initially. This is a relatively rare occurance.
Commissioner: A user who oversees and regulates a given league.
Private League: A league that must have teams assigned by a designated commissioner. These leagues are more active, and have a commissioner who helps oversee and regulate the league. Private league also have the option to change the league's salary cap and simulation speed, in addition to numerous other customizable features.
Zero Experience Player: A player who has yet to get 130 Plate Appearances or 30 IP in their careers.