Bivariate data

Bivariate data is a set of ordered pairs collected from the same individuals, which is what makes a scatterplot possible. For example, hours studied and points scored for three students, $(2, 5)$, $(4, 9)$, and $(6, 13)$, fall exactly on the line $y = 1 + 2x$, since every extra 2 hours adds 4 points. Both variables can be categorical instead, in which case the pairs are summarized in a two-way table rather than plotted. The whole point of bivariate data is association: you are asking how one variable moves with the other.