Oppression is malicious or unjust treatment of, or exercise of power over, a group of individuals, often in the form of governmental authority. There are many scholars who have attempted to define oppression usually by the types of harm suffered by those who are persecuted.

The word oppress comes from the Latin oppressus, past participle of opprimere, ("to press against", "to squeeze", "to suffocate"). Thus, when authoritarian governments use oppression to subjugate the people, they want their citizenry to feel that "pressing down", and to live in fear that if they displease the authorities they will, in a metaphorical sense, be "squeezed" and "suffocated". Such governments oppress the people using restriction, control, terror, hopelessness, and despair. The tyrant's tools of oppression include, for example, extremely harsh punishments for "unpatriotic" statements; developing a secret police force; prohibiting freedom of assembly, freedom of speech, and freedom of the press; controlling the monetary system and economy; and imprisoning or killing activists or other leaders who might pose a threat to their power.

Oppression also refers to the subjugation and marginalization of specific groups of people within a country or society, such as women, people of color, religious communities, citizens in poverty, LGBT people, youth and children, and more. This socioeconomic, cultural, political, legal, and social oppression can occur in every country, culture, and society, including advanced democracies.

There is no single, widely accepted definition of social oppression. Philosopher Elanor Taylor defines social oppression in this way:

Oppression is a form of injustice that occurs when one social group is subordinated while another is privileged, and oppression is maintained by a variety of different mechanisms including social norms, stereotypes and institutional rules. A key feature of oppression is that it is perpetrated by and affects social groups. ... [Oppression] occurs when a particular social group is unjustly subordinated, and where that subordination is not necessarily deliberate but instead results from a complex network of social restrictions, ranging from laws and institutions to implicit biases and stereotypes. In such cases, there may be no deliberate attempt to subordinate the relevant group, but the group is nonetheless unjustly subordinated by this network of social constraints.

Philosopher Jean Harvey, suggests the term "civilized oppression", which she introduces as follows:

It is harder still to become aware of what I call 'civilized Oppression,' that involves neither physical violence nor the use of law. Yet these subtle forms are by far the most prevalent in Western industrialized societies. This work will focus on issues that are common to such subtle oppression in several different contexts (such as racism, classism, and sexism) ... Analyzing what is involved in civilized oppression includes analyzing the kinds of mechanisms used, the power relations at work, the systems controlling perceptions and information, the kinds of harms inflicted on the victims, and the reasons why this oppression is so hard to see even by contributing agents.

A common conception of social oppression is seen as when a single group in society unjustly takes advantage of, and exercises power over, another group using dominance and subordination. This then results in the socially supported mistreatment and exploitation of a group of individuals by those with relative power. In a social group setting, oppression may be based on many ideas, such as poverty, gender, class, race, caste, or other categories.