What is considered asynchrony in programming languages ​​in general and in php in particular?

Question

PHP

php has PhpReact

in ruby ​​- EventMachine

python - asyncio

in c# - the concepts of asynchrony are substituted - multithreading ( link )

So what is considered asynchrony in programming languages ​​in general and in php in particular?

java - talking about Java in the context of asynchrony, they write about its work with sockets. So they are everywhere. Even in php.

I met the definition "Asynchrony (asynchrony) implies that the operation can be performed by someone on the side: a remote web host, server or other device outside the current computing device"

How adequate is it in your opinion?

Answer 1

https://ru.stackoverflow.com/a/816006/204271