This is something that might seem obvious to DBAs, but I was speaking with a developer this morning and realized there can be some confusion about what exactly single user mode means.
A database can be in multi-user mode, where multiple connections can be made to it, or single user mode, where only one person can connect to it. But here is the bit that can be confusing – single user mode doesn’t really mean single user – it means single connection. A database in single user mode can only have one connection to it, not multiple connections from the same user. The term single user is somewhat misleading here. A more appropriate term would be single connection mode.