  A linear code over $\mathbb{F}_q$ with the Hamming metric is called
$\Delta$-divisible if the weights of all codewords are divisible by $\Delta$.
They have been introduced by Harold Ward a few decades ago. Applications
include subspace codes, partial spreads, vector space partitions, and distance
optimal codes. The determination of the possible lengths of projective
divisible codes is an interesting and comprehensive challenge.
