(N/A) The word 'stoichiometry' is derived from two Greek words - $stoicheion$ (meaning element) and $metron$ (meaning measure).
Stoichiometry deals with the calculation of masses (and sometimes volumes) of the reactants and the products involved in a chemical reaction.
Stoichiometric calculation involves using a balanced chemical equation to determine the amounts of reactants required or products produced in a reaction.
For example,consider the combustion of methane:
$CH_{4(g)} + 2O_{2(g)} \rightarrow CO_{2(g)} + 2H_2O_{(g)}$
In this equation,the coefficients $1$ (for $CH_4$ and $CO_2$) and $2$ (for $O_2$ and $H_2O$) are called stoichiometric coefficients. These coefficients represent the molar ratio of the substances involved.
These relationships allow for the interconversion of data:
$mass \iff moles \iff \text{number of molecules}$
$\frac{mass}{volume} = \text{density}$