How can you understand this line of code?

Question

WordPress

I came across the following piece of code while parsing the plugin:

if ( ! defined( 'WPINC' ) ) {
    die;
}

Googled it. Information about defined is:

defined — Tests for the existence of the specified named constant

The author writes about it as follows:

Note the conditional statement at the bottom of the file. This means that the plugin file will not be directly accessible in a web browser.

But what is WPINC I can’t understand or find in any way.

Answer 1

WPINC
The name of the wp-includes directory. You cannot change this constant.
Default: wp-includes

Answer 2

This is a normal check.
Therefore, this page cannot be accessed directly - by url, it can only be accessed from the php code.