Validation is when you ensure that the data put into the database meets a certain rule.
There are different types of validation checks which can be performed on a database:
Presence check – does the field have to have a value entered?
Restricted choice check – the value entered has to be of a certain value (e.g. Mr / Mrs / Miss / Ms)
Range check – the value entered has to fall within a certain range (e.g. 0-100)