In computer science, coalescing is a part of memory management in which two adjacent free blocks of computer memory are merged.
Without coalescing, these blocks of memory stay separate from each other in their original requested size, even if they are next to each other.
Coalescing alleviates this issue by setting the neighboring blocks of freed memory to be contiguous without boundaries, such that part or all of it can be allocated for the request.
Among other techniques, coalescing is used to reduce external fragmentation, but is not totally effective.
Coalescence and related techniques like heap compaction, can be used in garbage collection.