Sometimes they're referred to as a throttle return dashpot, or just a carb dashpot. Even some older fuel injected vehicles have them. Though technically dashpots should be mechanical devices rather than vacuum. Still, you may have luck if you search that term
The picture that
@Craig 85 posted is a dash pot and it works differently to fix the same problem, engine popping on rapid throttle release.
Here is the basic issue, when you let off the throttle fast from a higher RPM the vacuum in the intake spikes very high. No air past the throttle plates, but the engine (as we know a big air pump) pulling hard. So what happens, the fuel that has puddled in the intake floats up and fires off causing the popping.
The dash pot method, holds the throttle so it will close slower, so no popping. The issue could be this dash pod will stick and cause wide open throttle.
Better (or maybe only safer) is the decel valve that lets some filtered air enter the intake so the vacuum doesn't spike high.
Many of the carburetor issues go away with fuel injection, but I still like carbs, I'm old school.