A kinematic joint is a connection between two or more links, which allows some motion, or potential motion, between the connected links.
Depending upon the number of links at the joint, a joint can be binary, ternary or quaternary. The mechanism shown in the above image is crank rocker mechanism and it comprises of 4 binary joints.
A binary joint comprises of 2 links and hence, 1 kinematic pair.
A ternary joint comprises of 3 links and hence, 2 kinematic pairs. So, 1 ternary joint is equivalent to 2 binary joints.
A quaternary joint comprises of 4 links and hence, 3 kinematic pairs. So, 1 quaternary joint is equivalent to 3 binary joints.