The difference between linux OS and linux Server

 I have did a reserach from the internet and make a sum as below.

Say linux OS is a software like windows .There are several different kinds of Linux, like CentOS, Debian, Ubuntu, and so forth. They all use the same base (the Linux kernel)

Whereas linux server is refer to the hardware (Computer case with mainboard and CPU inside) by

using one of these Linux operating systems.

Most Hits Q&A if desktop PC can run linux server ? Yes ,it can run,but for the learning and testing purposes ,if you want to serve the real work on the company then try to invest on the specific server will be a solution in a long term and pracicaly.

what is apacher?Apache is a piece of software available for most Linux operating systems (like you could install, say, Photoshop as a piece of software for Windows). Apache is what's called a web server. It resides on the physical server.

cross duty and function :

Apache is a webserver mainly developed to run on Unix/Linux type systems.

The difference between a server is that it's designed to serve something, hints the word (Serve). Basically not a desktop, but a desktop can play the roll as a server.

What is Ubuntu Desktop?

OS that can install on PC both desktop PC ,Laptop ,Server.
The Files and directories can be navigated by utilizing the file manager.
Ubuntu Desktop : having a Graphical User Interface (GUI), this Linux distribution relies on its command line known as “terminal.” The majority of commands that utilized the terminal for its execution can now use GUI as well.

What is Ubuntu Server?

The Ubuntu Server provides a whole operating system to use. It works with a command-line interface (CLI) rather than with GUI.  

Trend : New users who just switch from window OS some of them start to learn Ubuntu desktop for a simple and familiar with GUI similar to the window OS.