Flintlock pistols were so called because the lock uses a flint to strike sparks into the priming pan when the trigger is pulled. A small amount of gunpowder in this pan is ignited, which in turn ignites the main gunpowder charge in the barrel and fires the lead ball. Both the main charge and the ball were loaded from the front, or muzzle, of the barrel, after which the priming charge was poured into the pan--all very time consuming! Often the priming charge would burn, but fail to ignite the main charge--which is where we get the expression,  "a flash in the pan

“Caplock” or “Percussion Lock” pistols were so called because the lock system causes a percussion cap to be struck by the hammer when the trigger is pulled. Powder inside the cap ignites and this in turn ignites the main powder charge, which propels a lead ball from the barrel. Most (though not all) caplock firearms were loaded from the muzzle of the gun (muzzleloaders). The Caplock was a great improvement over the flintlock as it was less susceptible to weather-related misfires.