In natural language, the term "context" can be used in a sentence for example, "it depends on the context". Well, with SELinux, it does depend on the context! The context of a process is what identifies the process to SELinux. SELinux has no notion of Linux process ownership and frankly doesn't care how the process is called, which process ID it has and under which account the process runs. All it wants to know is what the context is of that process. Let's look at an example context: the context of the current user (try it out yourself if you are on a SELinux enabled system):
$ id -Z unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
id command, which returns information about the current user, with the
-Z switch ...