suppose we have a reaction as follows :
nA + mB ---> pC + qD
where n,m,p,q are natural numbers
these natural numbers are called stoichiometric coefficients .
Eg:
2P + 3Br2 ---> 2PBr3
here, 2, 3 from reactant side and 2 from product side are called stoichiometric coefficients
hope this helps...
