What does Bias mean?

[FAQ Team]

Think of a triode valve. You have a cathode, an anode and a control grid. The potential on the control grid can control the flow of electrons through the valve, but only when it is negative with respect to the cathode. If the grid is at zero volts or is positive, it is unable to repel electrons and hence cannot control the current flow.

It is therefore necessary to put a standing negative potential on the grid such that it remains at least slightly negative at the most positive expected excursion of the grid signal. This negative potential is know as the grid bias, or just bias. The bias also sets the quiescent current through the valve and hence it's operating class.