We use the term “task” to refer to any piece of code that needs to be run by a scheduler on resources provided by a resource management component.
Often, tasks will be packaged in containers, executed in a container runtime. They can be both long running deamons, like micro services - or short lived jobs.
The term “task” is used in Apache Mesos to refer to anything run by Mesos, other tools use different nomenclature which we will point out in the respective articles.