Sometimes I read about the term "scheduler" (offline-scheduler, online-scheduler,...) and then I see terms called "scheduling" (offline-scheduling, online-scheduling, preemptive scheduling, non preemptive scheduling). Currently I think, that scheduling is the real work and scheduler is just a umbrella term. Is that correct ?
This is more a question of English than computer science. For almost any regular verb (and "schedule" is a perfect example), the [verb]er is the thing that does the [verb]ing. The scheduler is the software that schedules.