why is it called BIASED?

"Biased" has about the same meaning in electronics as it has in general use: It notes a propensity/inclination. For example, I like the Sea Hawks, because they are a Northwest team. That is my bias.

In electronics, "biased" describes that the device is inclined to be in some state, such as on, off, or some point in between, where the force of the bias is a voltage. As I change the voltage magnitude and it's polarity, the device will be more or less inclined (biased) to a particular state, which a signal voltage can then modify.

Don