A weakness is an act, force, item that causes the individual affected to become feeble or uncomfortable. Weaknesses are also what people may not find to be their strong points.
A very common question asked during a job interview is 'What are your strengths and weaknesses? An example of an answer would be:
I feel as though my strengths are I work well with deadlines, I'm reliable, and I am not afraid of new challenges. My weaknesses are I'm not as articulate as I would like to be, and I shy away from public speaking situations.