Skepticism is doubt about something — you're just not convinced or can't totally believe it. If your brother is only four feet tall, you should view his claims that he can slam dunk a basketball with a lot of skepticism.
If you like to poke holes in other people's ideas, then you are full of skepticism. Some people follow a specific belief system that questions the truth of anything, but most people save their skepticism for certain things. Tabloids, Big Foot sightings, and over-eager used car salesmen should all be viewed with a little skepticism. On the other hand, gullible folks believe everything they hear and don't have much, if any, skepticism.