Key Skills or Skill set are now used as Tags.
They are used to highlight your profile to prospective recruiters.
Just like when you browse through google or a blog, you can see entries "tagged" by certain words, skill sets let the recruiter do the same.
Getting your skill set right will maximize your chances of coming up on the search.
These skills should also be easily cross-referenced with your experience, education, career contour.
And most importantly, these skills should be something that is valued for the position you are interested in. These skills are the criteria that get your resume shortlisted and some of these may even become your USP - Unique Selection Proposition
You should spend some time looking at what common terms are used to define success in your industry. What terms are used for nomenclature of skill sets.
Every industry has these. Some simple examples include, accounting, retail management, project management, auditing, research, customer relationship etc.
But I am suggesting that you dig deeper and look for words, terms that are maybe applicable to only your industry or even only to the role you are applying for or an interested in.
We have put together some examples.
See these to get the ball rolling:
Sample Skill Sets