When you're too excited to type in misspelled words to the point where you just simply hit the caps lock key and hit any letter you'd please. This is generally done very fast and it is an easy to get across "Hey, I'm excited and I have no idea what to say.
Usually it is used by fangirls to express love over a specific character in an anime or a video game
Also it occasionally starts or ends with a word.
"DID YOU SEE THE NEW EPISODE LAST NIGHT?"
"FGHDSJAKFGADSJKGHFSAJLDGHFSKLDAGHYES I DID!!! IT WAS SO AWESOMEGFDJLGHLKDGKFAL *foams at mouth*"
The uncomprehendable words the second person was saying is an example of over-excitement typing