An EXP Concentration License is a license that allows you to focus all experience gained on a single character in your formation, instead of splitting experience gained among your whole team. The license is applied to a specific formation slot, so you can use a single EXP Conc License on more than 1 character. For example, if you have a 3 hour EXP Conc Lic and want to use 1.5 hours of it on one merc and the other 1.5 hours of it on another merc, you could swap out the merc in the formation slot with the license via a merc room.