Uniform means the same. If your school has a uniform it means all the kids wear the same clothes. If you are told to make your handwriting uniform, they want your letters to be the same shape and size over and over.
When you break uniform down, you'll see uni for one, and form, for shape––things that are uniform have the shape. If you are building a Zombie Army, it's more fun to create zombies who are not uniform. Some can wear shredded shrouds, others can wear whatever they find. Some walk just fine, others leave body parts wherever they go.