Term: Caster Levels

Caster levels, or spellcaster levels, are seperate level of progression from class level and character level. Caster levels define how how many spell slots a caster recieves, as defined by the Spellcaster Level Table.
Full Caster classes gain a 1:1 caster level with their class level, where Half Caster and Quarter Caster classes gain their progression (and spell slots) at 1:2 and 1:4 the caster level. The first caster level any character recieves is always 1 full level.
A class that offers spellcasting will say when Spell Ranks are available, but they are usually in line with the spell progression of the class.