A FOREIGN KEY is a database key that is used to link two database tables together. It is a field (or collection of fields or columns) in one table, that refers to the PRIMARY KEY in another table. The FOREIGN KEY constraint is used to prevent actions that would destroy links between tables.
Having such relationships between tables in the database is useful to maintain the integrity of the data in the database and prevents the mistaken insertion or deletion of data from the linked database tables.
However, In some cases where it is necessary to repopulate a high amount of data inside the database, the FOREIGN KEY constraint check can prevent the repopulation. For example, if you have created a staging copy of your website and made significant changes to it and want to push it live then the action could be blocked by the constraint check. This is because when you push the staging to live it tries to overwrite the data in some of the tables of your database that have the foreign key relation.
If this happens, the Staging tool will show a warning message and give you the ability to disable the check and push the staging copy again. You just need to click Try Again and the staging copy will be pushed with the FOREIGN KEY constraint check disabled. Skipping the check will not affect your databases or the FOREIGN KEYS in them.