KSA stands for knowledge, skills and abilities. These are the proficiencies and competencies required for a particular position or role; these are usually outlined in a job description for  both the professional and personal abilities required. 

Most job applications will require the applicant to write in a few words how their knowledge, skills and abilities fit the particular position they are applying for and this is why it is important that employers include it in their job description in order to attract the right set of candidates.