Question

Can you tell me what is Truthiness?

Answer 1

Seeming truthful but without any evidence..

Answer 2

That's a non-existent, made-up word.    It was used in a public appearance
several years ago by a high-up political figure, who meant to say 'truthfullness'. 
The word is used now to poke fun and derision at that public figure, or any other
equally pompous, clueless, or verbally challenged one.