Wort is the name given to the sugar rich liquid that is extracted from the mash prior to fermentation. Prior to the boil, when the hops have not yet bittered the wort, it is known as sweet wort. After the boil but prior to fermentation, it is known as bitter wort since the beta acids from the hops have imparted a bitter flavor upon it.

 

A photo of sweet wort being transferred from the mash tun to the boil kettle after sparging had completed:

Wort (Unfermented Beer) Being Transferred after sparging

Wort (unfermented beer) being transferred after sparging.