gear shift

Short definition from Wiktionary

Noun

1. 1
   That part of a gearbox involved in changing gear, including the lever and the forks attached to it.
2. 2
   The lever or other interface a human uses to shift gears.
3. 3
   a stark change, esp. between considerably differently paced things (e. g. in a narration, topics on an agenda, music)