In general use
a relation is someone in the same family, and the relationship is
the connection between two members of a family such as aunt or cousin.
In mathematics the words are used in a similar way to mean the connection
between two sets of mathematical objects such as numbers or points.

For example,

2
is a factor of 4, and 6 is a factor of 72, which can be written
either as 2|4 and 6|72 or as D(2, 4) and D(6, 72).