Art definition and doubts

Can someone really give a definition of 'Art' ?. There are quite a few definitions of the word but nothing universal to every single thing perceived as art in the world. Its quite frustrating when someone calls what I produce 'not art'....some may call it illustration.....but its still art....isn't it?. The longer I go without creating something of great significance to myself and actually finish the bloody thing, the more doubts I have about my abilities and calling myself an artist.