Webster defines competent as:

1. proper or rightly pertinent
2. having requisite or adequate ability or qualities : fit <a competent teacher> <a competent piece of work>
3. legally qualified or adequate <a competent witness>
4. having the capacity to function or develop in a particular way; specifically : having the capacity to respond (as by producing an antibody) to an antigenic determinant <immunologically competent cells>

Incompetent is defined as:

1. not legally qualified
2. inadequate to or unsuitable for a particular purpose
3. a: lacking the qualities needed for effective action b: unable to perform a function properly <incompetent heart valves>

I define competence as being capable of doing the job and incompetence as being incapable of doing the job.