Discrimination is the prejudicial and/or distinguishing treatment of an individual based on their actual or perceived membership in a certain group or category, “in a way that is worse than the way people are usually treated.”[1]
It involves the group’s initial reaction or interaction, influencing the individual’s actual behavior towards the group or the group leader, restricting members of one group from opportunities or privileges that are available to another group, leading to the exclusion of the individual or entities based on logical or irrational decision making.[2] Discriminatory traditions, policies, ideas, practices, and laws exist in many countries and institutions in every part of the world, even in ones where discrimination is generally looked down upon. In some places, controversial attempts such as quotas or affirmative action have been used to benefit those believed to be current or past victims of discrimination—but have sometimes been called reverse discrimination themselves. / Employment discrimination (or workplace discrimination or labor market discrimination) is discrimination in hiring, promotion, job assignment, termination, and compensation. It includes various types of harassment.
Many jurisdictions prohibit some types of employment discrimination, often by forbidding discrimination based on certain traits (“protected categories”), such as gender, race, ethnicity.Earnings differentials or occupational differentiation is not in and of itself evidence of employment discrimination. Discrimination can be intended and involves disparate treatment of a group or unintended, yet create disparate impact for a group.

Source: http://en.wikipedia.org/wiki/Discrimination
http://en.wikipedia.org/wiki/Employment_discrimination