What does mod4 mean?

"Mod4" refers to the mathematical operation of taking the remainder after division by 4. It is commonly used in various contexts, such as computer science and number theory, to determine equivalence classes of integers. For example, when calculating (7 \mod 4), the result is 3, since 7 divided by 4 leaves a remainder of 3. Thus, numbers can be categorized based on their remainders when divided by 4.