what does exactly width 640px in function.php means?

hello,

I see this code in function.php

function auto_repair_content_width() {
	$GLOBALS['content_width'] = apply_filters( 'auto_repair_content_width', 640 );
}
add_action( 'after_setup_theme', 'auto_repair_content_width', 0 );

I read this article about the width 640:

It is a theme feature which helps us to control our content width for images, videos and embeds. If you used _s starter theme or browsed through any official WordPress theme, you saw it in the functions.php. In today’s responsive design, it is not the most necessary tool for the images but still useful because of the other media formats.

An excellent addition is that after the theme activation, it is also set the large image size to this value. It is also accessable for plugins. If you want to build a valid theme –?checked by Theme Check?– you should set up this parameter.

my question is :

I have image with width 700px and text on its right side with width 700px on screen with width 1920 pixels.

what 640px means here. is this means that wordpres wil take 700px width automatically to 640px width?

or I have to change 640px to 700px when I want to use an image or text that is wider than 640px?

thanks