A 5225 parenting schedule, is one in which one parent gets Wednesday and Thursday overnights, one parent gets Monday and Tuesday overnights, and Friday, Saturday, and Sunday overnights alternate between the two parents. This schedule is often preferred by child custody professionals, especially for school age children.
The graphical depiction above helps you understand where this schedule gets the name, 5225. This schedule may also be named with dashes, 5-2-2-5, with slashes 5/2/2/5, or maybe be called 2255 or 5522. All of these names refer to the same parenting schedule. The result of the schedule is that Parent 1 gets 5 days in a row, then Parent 2 gets 2 days, then Parent 1 gets 2 days, and then Parent 2 gets 5 days, thus 5225. The total schedule is 14 days, and the schedule gets repeated throughout the year.
There are other ways of doing 50/50 custody, this just happens to be the most common one.