proportional relationships – the relationship among a group of ratios that are equivalent.
constant of proportionality – the unit rate in a proportional relationship.
coordinate plane – a two-dimensional space formed by two perpendicular number lines called axes.
ordered pair – a pair of numbers (x, y) that describes the location of a point on a coordinate plane.
origin – the point (0,0) where the x-axis and y-axis intersect on a coordinate plane.