In chess, "space" is a type of positional advantage in which one player has more squares to which they can move their pieces than the other player. Creating space, gaining additional space, and denying one's opponent space are all important parts of playing "positional" chess.
In earlier time periods, chess players did not pay so much attention to the concept of space. However, this changed with the positional chess revolution of the late 1800s and early 1900s. Even so, space was considered less important than other types of positional advantage and material advantage. However, space has become more and more important over time in chess. In recent years, so-called "super GMs" and advanced neural network chess engines such as Alpha Zero have increasingly shown a willingness to sacrifice other advantages and even material simply to gain more space.