From Wikipedia:

In sociologypost-materialism is the transformation of individual values from materialist, physical, and economic to new individual values of autonomy and self-expression.

The term was popularised by political scientist Ronald Inglehart in his 1977 book The Silent Revolution, in which he discovered that the formative affluence experienced by the post-war generations was leading some of them to take their material security for granted and instead place greater importance on non-material goals such as self-expression, autonomy, freedom of speech, gender equality and environmentalism. Inglehart argued that with increasing prosperity, such post-material values would gradually increase in the publics of advanced industrial societies through the process of intergenerational replacement.

Post-materialism is a tool in developing an understanding of modern culture. It can be considered in reference of three distinct concepts of materialism. The first kind of materialism, and the one in reference to which the word post-materialism is used most often, refers to materialism as a value-system relating to the desire for fulfillment of material needs (such as security, sustenance and shelter) and an emphasis on material luxuries in a consumerist society. A second referent is the materialist conception of history held by many socialists, most notably Marxand Engels, as well as their philosophic concept of dialectical materialism. The third definition of materialism concerns the philosophical argument that matter is the only existing reality. The first concept is sociological, the second is both philosophical and sociological, and the third is philosophical.

Depending on which of the three above notions of materialism are being discussed, post-materialism can be an ontological postmaterialism, an existentialistic postmaterialism, an ethical postmaterialism, or a political-sociological postmaterialism, which is also the best known.