spin-off

Short definition from Wiktionary

Noun

1. 1
   An offshoot.
2. 2
   An incidental benefit or unexpected pay-off.
3. 3
   A by-product.
4. 4
   A fictional work where the protagonist was introduced in a preceding work or at least shares the same setting, often in a different aspect.
5. 5
   The formation of a subsidiary company that continues the operations of part of the parent company; the company so formed.

Verb

1. 1
   To create (something) as a by-product or a secondary derived work.