Deg is welsh slang and is used to describe the feeling of or something being amazing/ten out of ten. Deg in the welsh language is ten. The term started being used April 2011 in the South Wales region of Torfaen. Eg. I'm feeling so Deg today sunbathing. Omg that guy is sooo Deg. You look proper Deg in that dress. It is the equivalent of the Essex based term Reem. Feeling Deg, Looking Deg, and being Deg.