What is meant by the phrase "server part"?

Question

PHP

Hello!
I am a php, java programmer. I already know these languages ​​quite well. I wrote small applications in java. And in php I developed a file storage and a bunch of small projects for practice.
But still I don't understand what "Server part" and "Client part" mean . From design to implementation of the program, I did everything myself.
Explain, please.
Previously in the team, he did not work in large projects.

Answer 1

The server part is what is performed by the server, the client part is what is performed on the client side (browser, application, etc.). PHP runs on the server side, JS runs on the client side

Answer 2

The server part is also called backend, the client part is called frontend.
It turns out the backend - the "reverse side" which is not visible to the user, the frontend - "turned to face the user" - the client

Answer 3

server on the server, client on the client.