A family of Microsoft relational database management systems designed for ease of use.
You already got the answer you were looking for, but I want to explain why it is "Admin" for everyone.
It's because Access traditionally (up to A2003) had a security system called Workgroup Security where by default the current user was Admin. You could create other users in that system, and give them certain rights.
That system was done away with, but since it is so ingrained into the code, and not worth fixing, and not worth breaking existing applications, they just left that in, with the default user. Nobody uses it anymore.