What is a collation?

I updated Matomo to 5.1.2, and I miss one configuration : collation is empty. What is what, and what can I put?

You database connection is configured without an explicit collation. Please update [database] collation = '' in the “config/config.ini.php” file with the collation to be used, to ensure all database features work as expected.

Hi @thomasbnt
You’ll find some hints there: