In math and especially statistics, tally marks are used to count or record the frequency of an item. You could for example, use the tally marks shown below to record a score of 8.
Notice how the first four marks are drawn vertically. Then a diagonal mark, drawn across the previous four marks, is used for the fifth mark.
When the frequency of an item is at least five, the tally marks are organized by making one or more groups of five marks. We do it like that to make the information easier to read and count.