There are multiple definitions - click on the translation that matches your context.

Vertragsergänzung

Substantiv

full

addendum

noun

Comparative law notes

Austria

We recommend inserting the word "contract" before "addendum" or "supplement".

Definitions of addendum

English

a piece of additional material added at the end of a book, document or a speech

You can include this provision as an addendum to your will.