The phrase "to sit on" means to hold or possess something, often in a passive manner. It can be used figuratively when someone is in control of an asset or has power over it without necessarily actively using it. For example, if one says that they are sitting on a piece of property, it implies that they own the land but may not currently be utilizing it. The phrase can also have negative connotations, as in "sitting on information" which means withholding important knowledge or keeping something hidden.