When using a function such as get_post() the information requested is stored in a wp_post object. Everything that WorPress knows about a post can be stored in a wp_post object.
WP_Post Objects contain the following data:
The WP_post object is used to store data about posts. This data can then be accessed by methods such as get_post to retrieve that data for use on pages.
In summary like you say just about every week WordPress knows everything. This is just another example of that. Everything there is to know about posts on your site can be found by accessing the WP_Post object.