user

n. Someone who uses a computer system. Within the conventional
client/server paradigm there are two classes of people: those who
administrate the system and those who use it.

The term user is very conventional, going back to the early days
of time-sharing mainframes, but may be controversial in some contexts
due to having other negative associations, such as "drug user" or
someone who exploits other people for cynical and self-serving reasons,
as in "he was just a user". A possible alternative to user is
"member".