66b "Cut" Vav
The letter vav in the word Shalom at the beginning of Parshas Pinchas (25:12) is ketia (cut). What exactly does a cut vav look like?
Some say it is a short vav, and the bottom is cut off, but we must make it longer than a yud (Minchas Shai Bamidbar 25:12). Others say it is a full-length vav, but the leg of the vav is not continuous - the bottom of the vav is cut off from the rest of the vav (Ritva here). Some say it is a regular vav but written small (like the small aleph in Vayikra 1:1) (Meiri Kiryas Sefer 2:1 under "vehaktanos"). Some say it is written like a yud (Baal Haturim 25:12, Maharsha Kiddushin Chiddushei Aggados 66a s.v. Vav). These shitos are brought in Encyclopedia Talmudis "Vav" part 2.
Rambam and Shulchan Aruch do not mention this law, likely because if the vav was written regularly we would not change it.
See Shut R' Akiva Eiger 75 and Mossad Harav Kook Ritva Kiddushin 65b footnote 669.
This image shows a short vav and two ways of having a cut in the middle of the vav. From Encyclopedia Talmudis.