A ban occurs when a person has committed a grave offence like overstaying or making false representations in a visa application. When a government issues a ban, there is a mandatory refusal period until the ban is lifted, so attempts to enter the country or apply for a visa will fail. Nearly all the developed nations have some sort of banning regime, and many countries have agreements to share information about the subject.

Cancelled uk visa at the point of entry (with Removal form IS82C)

Sister visiting the UK visa refusal

UK Visit Visa - Possibility of refusal due to Deception

UK Visit Visa Refusal (Deception) and Reapplying Procedure

Circumventing a ban from the UK using another passport with a different name and dates of birth?

What can I do to lift a 10 year ban for making a mistake in my UK visa application?

I overstayed and was deported from Taiwan, how long am I now banned for?

UK Visa Refused for Deception; How to Tell if a Ban has been placed?