What does DeleteConstraintException mean?

I get the following error when deleting data:

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Cannot delete - bound by delete constraint on User log activity

An object class “User log activity” exists, and it has a property referencing the Object Class you are trying to delete. This reference property has Delete Rule: Delete Constraint. This means, if any “User log activity” is pointing to the data you are trying to delete, this error will occur (and the Delete will be aborted).

Solution: Change Delete Rule to “None” or “Cascade Delete”. Or, delete the other data (User log activity) first.