To quickly and violently cut something is to slash it. Sword fighters in a play might just clank their swords together, though they seem to slash each other. After the play is over, the snack stand might slash the price of popcorn.
A vandal might slash the tires on people's cars, and a baker will sometimes slash the top of a loaf of bread. Both use a sharp knife, and make sweeping motions as they cut, but the similarities end there. Figuratively, slash can mean "reduce," so a sale at your grocery store might be announced with a sign reading "We slash prices!" This figurative meaning dates from the turn of the 20th century.