How big is it? It could be a chocolate mould, or a jello/jelly mould... I doubt it can go in the oven though. Microwave maybe.
It is 8 " long and 43/4 " wide
It looks to me to be a jello or chocolate mold.
There is a slight possibility it's a MW cake pan but it looks heavier/ticker those.
If it's a jello mold I bet it could be used in the MW.