A term used in the video game industry, hitscan, or hitscan weaponry refers to a simple technique where you determine whether a target is hit by the weapon or not. Simply said, at the exact moment the player pulls the trigger, the game will check whatever is at the other end of the reticle and mark that target 'hit'. This means there are no other forces such as gravity etc that impact the shot - due the simple nature of this calculation (a straight line) it is often used with most weaponry in (modern) FPS's. Other, more complex calculations with projectile, take bullet speed, gravity, and other forces into account, which means that the bullet doesn't go in a straight line per se, and doesn't impact instantly.
The Half Life 2 SMG uses a Hitscan technique to determine whether it hits a target or not, but the Crossbow fires a projectile which uses a more complex calculation and takes many variables into acccount.
A game with the object of reaching Hitler's Wikipedia page by clicking on "Random Article", then clicking links in that article to get to other articles, until eventually you can find a link to Adolf Hitler's page. There are rules against using the "find on this page" option in your browser, and there is sometimes a time limit on how long you can spend on each page. Your score is determined by your number of clicks before clicking on Hitler's page. If you reach Hitler's page by clicking on "Random Article", you win the game forever and are probably Jesus.
me: Yo, this computer class is so boring, lets play that Hitler Wikipedia game.
you: okay...*click*...OH MY GOD HITLERS PAGE CAME UP WHEN I CLICKED RANDOM ARTICLE!!!
me: HOLY JESUS!!!!!!!!!