subindex
Noun
Meaning
A number or mark placed opposite the lower part of a letter or symbol to distinguish the symbol; thus, a0, b1, c2, xn, have 0, 1, 2, and n as subindices.
Source: Webster's dictionaryDerivatives
Examples
The new-export-orders subindex, a gauge of external demand, dropped to 28.7 in February from 48.7 in January.
The employment subindex remained in negative territory for the sixth consecutive month, even running weaker than the previous month.