When used as a noun, the word career usually means your profession or line of work, pursued over a number of years. It's not the same as a job, which can be as long or short as you like (you can have a job even just for a day). Also, if you talk about your career it implies that it is important to you; that you are thinking about progression, promotion, further development etc and not just going to work to earn money.

It comes originally from the Latin phrase via cararia, which means a track for wheeled vehicles to travel on - so there is the idea of a career as a road or path in life. We still talk about a 'career path' today.

As a verb, career also has another meaning: To move very fast, often in an uncontrolled way. For example, you could say 'The car careered down the hill and crashed into the hedge'.