Final answer:
A subscript in chemistry is a small number or symbol written below the baseline and to the right of an element symbol to indicate the number of atoms of that element in a compound or the number of electrons in a subshell.
Step-by-step explanation:
The 1st definition of a subscript in chemistry is a small number or symbol written below the baseline and to the right of an element symbol.
It indicates the number of atoms of that element in a compound or the number of electrons in a subshell.
For example, in nitrogen dioxide (NO2), the subscript 2 indicates that there are two oxygen atoms for every one atom of nitrogen.