Wikipedia - Stoichiometry stoichiometric number, $$\nu$$

https://doi.org/10.1351/goldbook.S06025
A chemical reaction of known @S06026@ can be written in general as: $a\text{A}\,+\,b\text{B}\,+\,...\rightarrow\,...\,+y\text{Y}\,+\,z\text{Z}$ For the reaction products Y and Z the numbers $$y$$ and $$z$$ are known as the @S06021@ numbers, $$\nu _{\text{Y}}$$ and $$\nu _{\text{Z}}$$, for Y and Z respectively. For the reactants the @S06021@ numbers are the negatives of the numbers appearing in the equation; for example the @S06021@ number $$\nu _{\text{A}}$$ for the reactant A is $$-a$$. In other words, the @S06021@ numbers are positive for products and negative for reactants.
Sources:
Green Book, 2nd ed., p. 42 [Terms] [Book]
PAC, 1996, 68, 149. (A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)) on page 187 [Terms] [Paper]
PAC, 1996, 68, 957. (Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)) on page 993 [Terms] [Paper]