"BLT" was the nickname given to B'Elanna Torres by Max Burke when the two were dating in the late 2360s. The nickname was based on the sandwich ingredients – bacon, lettuce, and tomato – which were also Torres' initials.
When Tom Paris learned of this, he became slightly jealous of Torres and Max's relationship. To "rub it in" a little, Harry Kim ended the conversation by referring to Paris as "Turkey Platter." (VOY: "Equinox")
Burke continued to refer to her by that nickname after his ship, the USS Equinox, encountered Torres' ship, the USS Voyager, in the Delta Quadrant in 2375 and 2376. (VOY: "Equinox", "Equinox, Part II")