To me it means used by employees of a company....usually standardized equipment which is dictated by the IT department.
There are small businesses and there are SMB...small to medium businesses. Then there are large businesses and very large businesses. Above that there is the enterprise...Bank of America, Home Depot, Wacovia, GE...you get the picture. Companies whose data protection requirements are phenomenally huge and their tolerance for downtime is a big fat ZERO.
“Enterprise” means larger businesses and corporations and includes a centrally controlled internal network. “In the enterprise” - in oversimplification - means “on that internal network.
Some people consider any organization with an Active Directory domain an enterprise network but that’s an overly narrow definition.
enterprise=business use