[lma21]

I've always used the term Coalescing in the past: https://en.wikipedia.org/wiki/Coalescing_(computer_science)

[ultrafez]

I've seen the term "request coalescing" used to refer to a technique to minimise the impact of cache stampedes. Protects your backend systems from huge spikes in traffic caused by a cache entry expiring.

[joeframbach]

And I've used coalesce to describe Array.prototype.reduce and Object.assign as well.