A hot plate was a small device upon which food could be cooked.
In 2151, Hoshi Sato offered to cook something for Malcolm Reed on a hot plate she had in her quarters. (ENT: "Silent Enemy")
In 2365, William T. Riker used a hot plate, courtesy of Data and Geordi La Forge, to prepare an 'Owon egg omelette for breakfast for themselves, as well as Katherine Pulaski and Worf. (TNG: "Time Squared")
In 2371, Benjamin Sisko used a hot plate to prepare blackened redfish for a dinner made for the senior officers on Deep Space 9. (DS9: "Equilibrium") Later that year, he used the hot plate again to prepare chicken paprikash for himself and his son, Jake. (DS9: "Family Business")