what mean radio?

Answer 1

It's a tool where you use it in the case when you want the end user to select only one of the option in your form.

Answer 2

The radio input is where you can select one option out of many. Syntax: <input type="radio" name="GROUP_NAME"/>

Answer 3

Im not sure what you mean

Answer 4

Radio — variants to answer, like: choose one: red, blue or green