Contribution/contributor license agreement. It’s a document that transfers the copyright from the original author - developer submitting a patch or PR - to the project owner, e.g. FUTO. If FUTO required CLA for all Immich contributions, then FUTO would own the copyright for all the source code of Immich. This allows FUTO to relicense Immich under a different license, other than GPL, for whatever purpose, without asking anyone. For example they could make modified Immich versions for sale, or sell the Immich source code to third parties under EULA or any other license.