A “session” cocktail is a drink that typically contains no more than .75 oz (or around 22.5mL) of a strong base spirit, perhaps lightly bolstered with lower-proof spirits.
This Session Margarita is a perfect example of this formula, with a smaller measure of tequila skewed nutty and warm against dry manzanilla sherry. It was featured in the excellent encyclopedia Session Cocktails from the editors of PUNCH magazine.