External fragmentation is a type of fragmentation that occurs in operating systems when there is enough total memory to satisfy a request, but the total required memory is not contiguous. It happens when a dynamic memory allocation algorithm allocates some memory and a small piece is left over that cannot be effectively used. The unused spaces formed between non-contiguous memory fragments are too small to serve a new process, which is called external fragmentation. External fragmentation occurs when the total memory is divided into memory partitions of variable size, and the size of these partitions depends upon the sizes of the processes. External fragmentation can be reduced by compaction or shuffling memory contents to place all free memory together in one large block. Paging is another solution to avoid external fragmentation.