(Seemingly) Stupid questions FTM ask

Ceyonia • 22. Married. Mommy of Titan Amari Smith 😌.
Okay, there's no such thing as a dumb question, and as a first time mom you can't possibly know everything . Heck, even women who have been moms for years don't know everything . 
My question : what's the difference between a onesie & sleeper because I honestly thought they were the same thing . 
Feel free to ask questions as well, & ladies don't be rude please. 😉