Is the urbandictonary website for defining names real or fake?

Oh it's real alright but the definitions are more for pop culture vocabulary. For example if you want to know what /Ho/ or /dyke/ means then UB is bang on for a definition. If you want to know what /arbiter/ or /aglet/ means then UB is not your friend, you need a proper dictionary like Collins, Oxford, Mirriam-Websters, etc.
The urban dictionary is half joke entries and half satirical/pop culture definitions. It is the modern equivalent of The Devils Dictionary. A wonderful book containing satirical entries of modern words that was first published back in the 1800s.