Pattern condensed representations are an important concept in inductive databases. They aim at summarizing the information contained in a set of patterns. This paper is not an exhaustive survey of the 20 years of proposals on condensed representations but rather a general overview. We propose a simple formalism modeling a large part of the exact and approximate condensed representations. Through this modeling, we show that many of the condensed representations are based on the same foundations, we highlight the compression and generalization sides of the condensed representations and we describe several trends. Finally, we discuss the current extents of the work on condensed representations within pattern mining.