In the context of Social Security disability, the touchstone for job skills is Social Security Ruling 82-41. That Ruling states:
A skill is knowledge of a work activity which requires the exercise of significant judgment that goes beyond the carrying out of simple job duties and is acquired through performance of an occupation which is above the unskilled level (requires more than 30 days to learn). It is practical and familiar knowledge of the principles and processes of an art, science or trade, combined with the ability to apply them in practice in a proper and approved manner. This includes activities like making precise measurements, reading blueprints, and setting up and operating complex machinery. A skill gives a person a special advantage over unskilled workers in the labor market.
At a Social Security disability hearing, a vocational expert may testify regarding a claimant's acquired job skills. In my experience, vocational experts can be cavalier about what exactly constitutes a skill. I have had disability hearings where vocational experts named things like making change and dealing with the public as acquired job skills from a cashier job. To me, those things do not rise to the level of skills, as defined by the Ruling.
What constitutes a skill is important, because the existence of transferable skills can doom your Social Security disability claim.