That is the volume of trades that went through but not at the bid or the ask. Usually they are trades that split the bid and ask but sometimes they are trades above or below the split. The t trades fall into that catagory I think. I couldn't tell if that was the case today 'cause the Java thingy wasn't working today.
Take my advice with a grain of salt. (preferably many grains distributed around the rim of a margarita glass.) I am not a stock professional, trade at your own risk!
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