Collinear refers to the property of a set of points lying on a single straight line. In geometry, collinearity is the property of a set of points lying on a single line. The term collinear is derived from the Latin words col and linear where col stands for together and linear means in the same line. Collinear points may exist on different planes but not on different lines. In coordinate geometry, in n-dimensional space, a set of three or more distinct points are collinear if and only if the matrix of the coordinates of these vectors is of rank 1 or less. In statistics, collinearity refers to a linear relationship between two explanatory variables. Two variables are perfectly collinear if there is an exact linear relationship between the two, so the correlation between them is equal to 1 or −1.