What is the 'd' in the literal 12d called?

I feel like I should know the answer to this, but I don't.

What is the type character on a numeric literal called?

double myDouble = 12d;
float myFloat = 10f;

I wanted to find a complete list of them today, but couldn't come up with what to ask Google to search for.

EDIT

Found a decent list if anyone is interested

http://www.undermyhat.org/blog/2009/08/secrets-and-lies-of-type-suffixes-in-c-and-vb-net/