Machete

The Machete is a new close combat weapon introduced in Left 4 Dead 2.

The machete, like every other melee weapon, is not really meant to be used against Special Infected, because using it on a Boomer would cover you in bile, and killing a Spitter would leave you right in the middle of the goo. It would also take time to get to a Charger, Jockey, Hunter or Smoker. Against a Tank or Witch it would do little to no damage. On common infected, it easily hacks off limbs. This is one of the most brutal weapons in Left 4 Dead 2, producing a lot of close-up gore. This weapon can also be used on a group of common infected, but if the group is too large, it will kill the ones in the front while simply knocking the others back to be dealt with later.

Trivia

 * The weapon could possibly be a reference to the movie 28 Days Later, where the main female character Selena wields a machete. This is likely as the Infected in this movie are almost identical to the Common Infected in Left 4 Dead, and were most likely used as a reference. It could also be a reference to Jason Voorhees from the Friday The 13th series, who is most commonly seen wielding a machete.
 * On the movie poster for "Dead Center," Coach is wielding a machete
 * Even though this is a long, bladed weapon that is more than capable of decapitation, you cannot decapitate a Witch with this weapon, only the Axe and Katana are capable of doing so. This isn't entirely a bad design flaw, as the machete isn't as powerful as other bladed weapons.

Exernal Links
http://www.youtube.com/watch?v=vors0yz9EsQ- The machete gameplay.