What is meant by Multisite in WordPress?

Question

I am a newbie in WordPress not totally but 6 months. I am confused with MULTISITE. I want to know that what is it, correct me if I wrong => is it a way to create a multi purpose site/theme easily means in default WordPress we can create a blog or a business site etc, but by using multisite functions that WordPress provide, I think it that we can create a multipurpose website easily again correct me if I wrong. Or is it used for something else if it is

1. then what is that,
2. what is the role of multisite functions,
3. what the can do (means what they can provide so that I can make my site/theme better),
4. are they useful for developers (means did I have to make my site/theme using these functions),
5. we can make secure site/theme,
6. the beginners need to also learn about multisite functions

Answer 1

Wordpress Multisite allows you to use one WordPress code installation to run multiple websites.

mywebsite1.com mywebsite2.com mywebsite3.com etc

All run from the same code, can share the same plugins, can share the same themes (but use different themes), share the same admin login (but different sites can be limited to different editors), keep all data in the same database (but stored in different, not-shared tables).