Bias is a tendency to lean in a certain direction, either in favor of or against a particular thing. To be truly biased means to lack a neutral viewpoint on a particular topic. Somewhere along the line, bias took on a negative connotation. We tend to think it's a bad thing but that's not always true.
If you're biased toward something, then you lean favorably toward it; you tend to think positively of it. Meanwhile, if you're biased against something, then you lean negatively against it; you tend to think poorly of it.
Truthfully, everyone has biases, preferences and prejudices. Let's take a moment to break down some of the connotations surrounding this issue and then dive into several examples of bias.