Bias has numerous meanings. It literally means diagonal or slant.
Bias is a DC voltage level added to an AC signal which is to be amplified. This is done to put the AC signal within the amplifying transistor's linear operating area.
Bias is also a name for a high-frequency sine wave added to an audio signal as part of the process of magnetic tape recording; it eliminates distortion that would otherwise be caused by magnetic hysteresis.
Bias means flaws in the collection, analysis or interpretation of research data that lead to incorrect conclusions. Sampling bias is a form of bias in which some members of a population to be studied are more likely to be selected than others, so that the sample does not accurately reflect the population. A particular form of sampling bias is self-selection bias, in which the members select themselves, so that any conclusions drawn from the sample are biased in favor of those who would be more likely to choose to participate. Another form of sampling bias arises from cherry picking the members to be included in the sample.
A bias is sometimes defined as a violation of a normative standard. For example, the fact that people will be less likely to trade an object they already have for another one—regardless of which object they initially possess—violates the normative standard that preference for an object should not be swayed by what is already possessed. A common form of bias in psychology is cognitive bias, which is a mental error caused by our simplified information processing strategies.
Studies of biases in psychology have shown that many principles assumed in economics are incorrect (Kahneman 2003) by illustrating that the notion of a free rational agent is idealistic.
- It is not always the most well-credentialed and experienced individual, who will correctly interpret confusing results or data. The confusion likely results from inadequate or faulty initial assumptions, and the learning and experience behind the credentials make it hard for the “expert” to question those assumptions. 
In works describing a potentially controversial topic, bias refers to the tendency of an author who holds a particular viewpoint to express that viewpoint (whether intentionally or subconsciously) in his work. This typically goes against the ideal of compendiums which are meant to be neutral, such as encyclopedias. For example, if an article on abortion is written by someone who supports it, it will likely be biased towards that viewpoint, and vice versa.
- ... far too much historical scholarship consists of contorting the evidence to fit ideological models. The worst examples of such contortions are the Nazi and Communist histories of the early- and mid-twentieth century.