A person is "biased" if they are not able to give an objective opinion. A person might be "biased" because:

• They will make money from one of the choices but not the other.
• They already have strong ideas about the topic.
• They have a relationship with one of the people who is trying to persuade them.

For example, if you ask me "What's the best way to learn English?" then I will say that I am "obviously biased" because I think my website is the best way.