How can we define backbiting?

If something is really bothering you...Say you had a stressful day at work, or someone was unfair with you and this problem is really bothering you...if you discuss the details of this problem with your wife, and you tell her how you feel about the problem and how you feel that so and so person was unfair with you and has really upset you...is this considered backbiting? Where do we draw the line between stating the facts and backbiting? Sometimes I find it difficult to keep every single thing that involves a third party cooped up inside.