Concatenative Synthesis is where you take small chunks of sound and stick them together to produce an output. It is similar to [granular-synthesis], but rather than putting grains together randomly with the goal of producing textures or waves of sound, concatenative synthesis focuses on choosing the pieces carefully to produce carefully sculpted outputs.
It is very commonly used in [vocal-synthesis] with the different pieces of sound being different pieces of speech. This approach is used directly by [utau].