What is kosher gelatin? is it any different from the animal derived protein used in Jello?

That is a very complicated question. Entire books have been written about it.

The most simplistic answer is that it is any gelatin that has been deemed so by a qualified rabbi.

Not all fish gelatin is kosher and not all kosher gelatin is from fish. It could also be from animal hides.

Here's an article that may help http://www.oukosher.org/index.php/common/article/the_fascinating_story_of_kosher_gelatin_or_how_a_product_from_beef_can_be_u/

Kosher gelatin is derived from fish.