What does alligation mean?
The definition of alligation
Al`li*ga”tion, n.
Etym: [L. alligatio.]

1 The act of tying together or attaching by some bond, or the state of being attached. [R.]
2 (Arith.)
A rule relating to the solution of questions concerning the compounding or mixing of different ingredients, or ingredients of different qualities or values.

Note: The rule is named from the method of connecting together the terms by certain ligature-like signs. Alligation is of two kinds, medial and alternate; medial teaching the method of finding the price or quality of a mixture of several simple ingredients whose prices and qualities are known; alternate, teaching the amount of each of several simple ingredients whose prices or qualities are known, which will be required to make a mixture of given price or quality.