Well, I think of it as "the behaviors and beliefs characteristic of a particular social, ethnic, or age group", or at least that seems like words with a broad enough meaning to encompass what I think is "culture"... including how these behaviours and beliefs manifest themselves in the form of the arts (literature, music, visual arts, architecture etc.) as well as in "popular culture" i.e. what is seen in mainstream marketing, entertainment, lifestyles... also including prevailing/popular views, philosophies etc... it is too broad to be easy to define in any meaningful way.

It has happened to me to be in a state of serious misunderstanding with some people about the meaning of the word "culture". They said they liked "culture" and me too, yet we had nothing in common.