Heuristics and Biases are the ways human reasoning differs from a theoretical ideal agent, due to reasoning shortcuts that don't always work (heuristics) and systematic errors (biases).
See also: Affect Heuristic, Confirmation Bias, Fallacies, Predictably Wrong, Rationality, Your Intuitions Are Not Magic, Bias, Heuristic
“Cognitive biases” are those obstacles to truth which are produced, not by the cost of information, nor by limited computing power, but by the shape of our own mental machinery. For example, our mental processes might be evolutionarily adapted to specifically believe some things that arent true, so that we could win political arguments in a tribal context. Or the mental machinery might be adapted not to particularly care whether something is true, such as when we feel the urge to believe what others believe to get along socially. Or the bias may be a side-effect of a useful reasoning heuristic. The availability heuristic is not itself a bias, but it gives rise to them; the machinery uses an algorithm (give things more evidential weight if they come to mind more readily) that does some good cognitive work but also produces systematic errors....