The latest Video Developer Blog from the Pathfinder Online team has been released. In it, the team discusses the way that roles will be deployed during both Early and Open Enrollment. As the blog post indicates, role and class are used fairly interchangeably but there is a difference that the team seeks to identify in the video.
Character abilities may be associated with a "role", which is an analog to the tabletop "class" system, or they may not have a role association. You are free to mix and match the abilities your character earns, guided by the skills you are investing XP to train. Some players will focus their characters very strictly to progress along a "role" as quickly as they can. Others will want a more broad-based character and will gain a wider variety of new abilities. The advantage of the former strategy is becoming very effective in a narrow specialty quickly. The advantage to the latter is having the ability to do a wide variety of things even if the character isn't a master of any of them.
Check out the video below before heading to the Pathfinder Online site.