I've never seen anything like that in my life, but if I knew some things like the year, make (Buick, Pontiac, Oldsmobile), and size of the engine I could look it up. It would save you some time and help everyone greatly in the future if you would add your vehicles info to your profile. Click on your Avatar in the upper right. Go to Account Settings. Scroll down to vehicle details and write in your year/engine/transmission info. When you do that, we will all see it under your Avatar in your posts. This thread was also posted in the General Engine section which would cover anything from 1967-2002. If it appeared in a generation specific engine section, that would narrow down what you have there.
I'm not scolding you here, just trying to show how you can make things a bit more efficient in the future. This time around you had to wait for me to tell you "we need more information", and now I'm waiting on you to provide that, then you'll be waiting on me or someone else to actually offer an answer. ...that's all. Saves time and frustration. Always a good thing.
Looks like it could be a pulsation damper for fuel rail(s), but without knowing any info at all about the engine (as noted in the post above), I don’t even know if it’s an engine that even has fuel injection, and I could be 100% incorrect.