The phrase "concurrent users" refers to the number of people who are using a computer program or website at the same time. It measures the maximum number of users using the system simultaneously. Full definition
There is now limitless database size capacity and a limitless number of concurrent users in the database. (leesoftwaresupport.com)
The game surpassed 1.2 million peak concurrent users over the weekend. (shortpause.com)
It now has less than 1000 concurrent users on steam so the whole world hates the game not just «haters» or «people on the hate train». (indiewatch.net)