A coordinate system is a set of one, two, three or more coordinate axes. An axis and a unit segment form a coordinate axis. These axes cross in the point of origin. A coordinate system with perpendicular axes is called a perpendicular coordinate system. If such system has the same unit segment for each of the axes then it is called Cartesian coordinate system.
An axis OX is called the abscissa axis, an axis OY is called the ordinate axis.