A sulfonic acid is an oxoacid that has the following general structural formula.

In the most common sulfonic acids, R is either an alkyl group (alkanesulfonic acid) or an aryl
group (arenesulfonic acid).

eg. 1:

Using the symbol Ms, methanesulfonic acid can be shown conveniently as MsOH.

eg. 2:

Using the symbol Ts, p-toluenesulfonic acid can be shown conveniently as TsOH.