What Can I Say When There Is Missing Letters 1996 Cent

Looks like a mint error called a Grease Filled Die. Nice one Might bring a small premium to the right person.

In short, yes it is an error.
Sometimes dirt or grease can build up on a die and fill certain parts, so when a coin is struck with a filled die, this is the result. It is not a highly collectable variety such as a doubled die or RPM.
Errors are mistakes in the minting process, varieties are mistakes on the die itself which creates several coins that are the same.
These filled dies are pretty common and don't have a lot of added value. I keep them just because they are different.