What is exactly the event object? [duplicate]

Question

What is an event object? When is it executed? Why do we have it? For example:

1. when we use an anonymous function as in this example, the event object will not be renderPosts() function.

   window.addEventListener('DOMContentLoaded', () => renderPosts());
   
   const renderPosts = async () => {
     let uri = 'http://localhost:3000/posts?_sort=likes&_order=desc';
     const res = await fetch(uri);
     const container = document.querySelector(".blogs");```
   
   

2. when we do not use anonymous function as in this example, the event object will be renderPosts() function.

   window.addEventListener('DOMContentLoaded',renderPosts());
   
   const renderPosts = async () => {
     let uri = 'http://localhost:3000/posts?_sort=likes&_order=desc';
     const res = await fetch(uri);
     const container = document.querySelector(".blogs");```
   
   
   

I do not see the difference and not really understand it.