A wax melt is scented wax without a wick, warmed in a burner until it releases its fragrance. The base is usually paraffin, soy, or a blend, combined with fragrance oil at roughly six to ten percent by weight and poured into molds that let users snap off one portion at a time.
Because melts are warmed rather than burned, they behave differently from candles: the wax never disappears, scent strength depends heavily on warmer temperature, and the same piece can often be re-melted across several sessions until the fragrance is spent. Understanding those three facts explains most of the practical advice given to new users.