This is the concept of algebra, given a polynomial with one variable like x and y, the degree is the largest exponent of the variable;
Given the expressions;
4x^3-2y^3+5y^2-5y The polynomial has a degree of 3 (both y and x have an exponent of 3)
3y3--xy=3y^3+xy The polynomial has a degree of 3 also (y has an exponent of 3)