ProgrammingCircleJerk

I think this is referring to clients that are actively connected and transmitting / receiving data. For example, watching a video means you need a fairly constant connection to the server. 100 concurrent users would be able to begin watching a, lets say 10 minute video. For these 10 minutes, the server may not accept a new user. After 10 minutes, slots free up that can handle other users. Technically it is more complicated than this, involving bandwidth, number of cores / threads, databases, queries, etc which will limit how many users the service can handle, and connections can be made and broken to allow the service to serve a larger number of concurrent clients.

In the above example, you have 100 users every 10 minutes which is 14,400 users a day assuming 100% utilization