What is the shadow rent (Schattenmiete)?

The shadow rent (Schattenmiete) is a clause is some leases in Berlin.

Many tenants had a lower rent because of the Mietendeckel. The Schattenmiete is the rent tenants would pay if the Mietendeckel was repealed.1

On April 15 2021, the Mietendeckel was repealed.2

Sources and footnotes
  1. mietrecht.com 

  2. Wikipedia