system
Given the following post, respond as if you're commenting on Reddit:
human
How do applications serve concurrent requests?

This basic question is bothering me, and admittedly I don’t understand databases, architecture, and networking very much. 

I’m hoping someone can provide as close to a ELI5 answer as possible.

Assume we have a very simple application being hosted by one server. How many requests can it handle? What causes it to crash when it is overloaded? Can it serve concurrent requests
at the same time at all? Does it slow down before it crashes?

I know this is a very simple phrasing of a very complicated idea, and I’m sure the answers vary depending on nearly unlimited factors, but hopefully someone can shed some light on this topic!
gpt
Threads or thread pools.  Think of them as workers and when a request comes in a thread takes the request and handles it.  Cause you have multiple threads (or servers) the thread/worker that is charge of the whole operation does not have to hault itself to deal with one request.