Seat licenses go by many names including Personal Seat License or PSL, Stadium Builder’s License or SBL, and Charter Seat License or CSL. All are seat licenses that allow fans to buy season tickets, sell tickets, and sell the seat license. This is a change from the old days where the ability to buy season tickets was called “Season Ticket Rights” or STR. STRs did not give the fan the right to sell those rights and some also restricted fans from reselling their tickets.
The primary factor that causes teams to switch from STR to seat licenses is the cost of new stadiums. The secondary factor is the move away from publicly funded stadiums, which means teams must turn to their fans to finance new stadium construction.