An open connected set is called a region (sometimes also called a domain).
Region
Explore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Region." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Region.html
An open connected set is called a region (sometimes also called a domain).
Weisstein, Eric W. "Region." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Region.html