Halfoween

Halfoween is the holiday invented by Carly, Kayla, Sam and Freddie in the episode of the same name. It's essentially a way for the trio to wear costumes in April without waiting till October 31st, the actual date of Halloween.

Description
Halfoween celebrates the halfway point between the previous Halloween and the next Halloween, hence "half" in the name. To emphasize the half, many Halloween-related props are cut in half. Sam even cut the belongings of others in half such as Spencer's sunglasses or Gibby's cell phone.

Carly organized the first (and only) Halfoween party in her apartment, where the trio was purposefully fed voice-deepening candy by Nevel. As punishment, Nevel was dunked repeatedly in Spencer's Jerk Basket, a basket filled with prizes that Spencer used as a boardwalk game.

Halfoween has not made an appearance since, with its only appearance being iHalfoween.

Credits to

 * iCarly Wiki on Fandom