"Entry processes" usually means "concurrent connections". Its the number of web server processes running.
An include is not a separate process. A database connection IS a separate process, but NOT an "entry process". That is why they specify "entry processes".
Apache defaults to keeping a connection open for 15 seconds after the last request. So if you have twenty visitors in less than 15 seconds, you will hit the limit.
A client may open more than one connection at a time. e.g. a web browser may open one connection to load the HTML in, and when it gets to the first img tag open another to open download the image - and both stay open for 15 seconds. If each visitor opens two connections you will hit the limit at 10 visitors on 15 seconds.
DO you offer large file downloads? Download managers/accelerators often open multiple connections. Three simultaneous downloads with either connections each would go over your limit as well.
You may need to use different hosting. Neither of the hosts I use has this limit: one gives me my own event driven server instance (so one process handles multiple connections), the other is pay as you go based on traffic.