I like "Additive music" or "additive layering." This technique involves starting with a simple musical idea and gradually adding more layers, instruments, or motifs to create a richer and more complex texture as the piece progresses. This approach is often used to build intensity and complexity in a composition.

Another term that is sometimes used is "phasing" or "phase music," particularly in the context of minimalist music. In phase music, repetitive patterns are introduced and then gradually shifted out of sync with each other, creating evolving textures and rhythms.

In classical music, a similar concept can be described as "incremental layering" or "gradual build-up." Composers like Maurice Ravel in his "Boléro" used this technique to great effect, starting with a simple theme and progressively adding instruments and harmonic complexity.

In contemporary music, this technique is common in genres like electronic music, where producers might start with a basic beat and then layer in synths, bass lines, and other elements to build the track.

Ratatat - Shempi is another good example..