get(0) returns the first DOM element matched by the selector.

eq(0) returns a jQuery object containing the first DOM element matched by the selector.

In other words, $("selector").get(0) is equivalent to $("selector").eq(0).get(0).

The .get() method returns a DOM element at the given index.

The .eq() method returns a DOM element at the given index, wrapped in a jQuery object.

Another difference is that if you don't pass an argument to .get(), it will return an Array of the DOM elements in the jQuery object.