A stake was a pointy wooden object and one of the most effective ways to slay a vampire.
In order for the weapon to be effective, it must've penetrated the vampire's heart. However, vampires in possession of the Gem of Amarra would be rendered invincible, and immune to staking. A vampire could also become immune to staking by having its heart surgically removed, although this process certified the vampire’s death within about six hours.
Generally, any wooden object of a reasonable size could function as a stake (including broken chair legs, decorative bamboo sticks, tree branches etc.) but professionals tended to carry their own specially carved stakes. Agents of the Initiative along with Wolfram & Hart security guards and Special Opps each individually carried their stakes while dealing with vampire attacks, similar to how they would use a combat knife or nightstick.
Kendra Young once owned a individual stake which she nicknamed "Mr. Pointy". She then passed this on to Buffy before her death.
Along with vampires, stakes were also an effective weapon against species related to vampires, such as the Turok-Han and zompires.
Behind the Scenes
The prop stakes used in Buffy the Vampire Slayer were made of real wood, however, when it came to stabbing, stakes with a retractable points were sometimes used in action scenes to create the illusion of stabbing. There were also stakes cast in foam rubber and plastic.
There were two to three different stakes introduced per season.