According to Webster's Dictionary online:

Bias (adjective) is defined as:

a: BENT, TENDENCY

b: an inclination of temperament or outlook; especially: a personal and sometimes unreasoned judgment: PREJUDICE

c: an instance of such prejudice

d(1): deviation of the expected value of a statistical estimate from the quantity it estimates (2): systematic error introduced into sampling or testing by selecting or encouraging one outcome or answer over others