W/T just means you can select a player that can fill either your Wide Receiver or your Tight End spot. W/R means the player can fill a Wide Receiver or a Running Back spot. Many running backs are good receivers out of the backfield, so you may choose use to NO RB, but rather two WRs and W/R. You may have selected three VERY good receivers, so you may go with a two WRs and a W/T and eschew your TE.

It just gives you some flexibility with your lineup. In baseball terms, he would be the "utility player."

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Whenever I text "Barack," my phone suggests the word "Capable." I guess my my phone IS pretty smart.