What is Bias?

Legal Definition
Bias is an inclination or outlook to present or hold a partial perspective, often accompanied by a refusal to consider the possible merits of alternative points of view. Biases can be learned implicitly within cultural contexts. People may develop biases toward or against an individual, an ethnic group, a nation, a religion, a social class, a political party, theoretical paradigms and ideologies within academic domains, or a species. Biased means one-sided, lacking a neutral viewpoint, or not having an open mind. Bias can come in many forms and is related to prejudice and intuition.

In science and engineering, a bias is a systematic error. Statistical bias results from an unfair sampling of a population, or from an estimation process that does not give accurate results on average.

-- Wikipedia
Legal Definition
A particular influential power which sways the judgment; the inclination or propensity of the mind towards a particular object.

2. Justice requires that the judge should have no bias for or against any individual; and that his mind should be perfectly free to act as the law requires.

3. There is, however, one kind of bias which the courts suffer to influence them in their judgments it is a bias favorable to a class of cases, or persons, as distinguished from an individual case or person. A few examples will explain this. A bias is felt on account of convenience. 1 Ves. sen. 13, 14; 3 Atk. 524. It is also felt in favor of the heir at law, as when there is an heir on one side and a mere volunteer on the other. Willes, R. 570 1 W. Bl. 256; Amb. R. 645; 1 Ball & B. 309 1 Wils. R. 310 3 Atk. 747 Id. 222. On the other hand, the court leans against double portions for children; M'Clell. R. 356; 13 Price, R. 599 against double provisions, and double satisfactions; 3 Atk. R. 421 and against forfeitures. 3 T. R. 172. Vide, generally, 1 Burr. 419 1 Bos. & Pull. 614; 3 Bos. & Pull. 456 Ves. jr. 648 Jacob, Rep. 115; 1 Turn. & R. 350.
-- Bouviers Law Dictionary
Legal Definition
Inclination; bent; prepossession; a preconceived opinion; a predisposition to decide a cause or an issue in a certain way, which does not leave the mind perfectly open to conviction. Maddox v. State, 32 Ga. 587, 79 Am. Dec. 307; Pierson v. State, 18 Tex. App. 558; Hinkle v. State, 94 Ga. 595, 21 S. E. 601.

This term is not synonymous with "prejudice." By the use of this word in a statute declaring disqualification of jurors, the legislature intended to describe another and somewhat different ground of disqualification. A man cannot be prejudiced against another without being biased against him ; but be may be biased without being prejudiced.

Bias is "a particular influential power, which sways the judgment; the inclination of the mind towards a particular object." It is not to be supposed that the legislature expected to secure in the juror a state of mind absolutely free from nil inclination to one side or the other. The statute means that, although a juror has not formed a judgment for or against the prisoner, before the evidence is heard on the trial, yet, if he is under such an influence as so sways his mind to the one side or the other as to prevent his deciding the cause according to the evidence, he is incompetent. Willis v. State, 12 Ga. 444.

Actual bias consists in the existence of a state of mind on the part of the juror which satisfies the court, in the exercise of a sound discretion, that the juror cannot try the issues impartially and without prejudice to the substantial rights of the party challenging. State v. Chapman, 1 S. D. 414, 47 N. W. 4ll, 10 In R. A. 432; People v. MicQuade, 110 N. Y. 284, 18 N. E. 156, 1 L. In A. 273; People v. Welle, 100 Cal. 227, 34 Pac. 718. '
-- Black's Law Dictionary
Legal Definition
Prejudice. See 9 Am. St. Rep. 745.
-- Ballentine's Law Dictionary