If it's in your basement then no wonder it's not carbed and conditioned. I doubt it's above 70 degrees down there. You need the beer in the warmth for at least 3 weeks for carbonation and conditioing to take hold.
The taste of green beer is really any taste that doesn't taste like you feel it should, barring an infection whic would turn the beer sour, or oxydized which would give it a liquid cardboad taste, or nail polish which is usually from an infection.
In terms of "green beer" some describe beer that isn't ready as having a cidery taste, some describe a green apple taste, some just lifeless flavor, some say there's no hop character (which does pop once the beer is conditioned.) There's a lot of variables, but usually it just boils down to the beer doesn't taste like you're expecting it to taste....Like the beer you're used to.