Culture is the distinct ways that people living in different parts of the world classified and represented their experiences.
In the 20th century, "culture" emerged as a central concept in anthropology, encompassing the range of human phenomena that cannot be attributed to genetic inheritance. Specifically, the term "culture" in American anthropology had two meanings:
the evolved human capacity to classify and represent experiences with symbols, and to act imaginatively and creatively; and
the distinct ways that people living in different parts of the world classified and represented their experiences, and acted creatively.
Distinctions are currently made between the physical artifacts created by a society, its so-called material culture and everything else, the intangibles such as language, customs, etc. that are the main referent of the term "culture".
In the realm of User Expereince, the tag culture schould be treated as the distinct way people living in different parts of the world classified and represented their experiences. It is important to notice that the meaning of different colors varies greatly between different cultures. Questions having the culture tag regards everything about culture and differences between cultures in User Experience design.
Reference: Wikipedia - Culture