British Rail coach designations
In the original LNER coding system, S stood for "Second", an intermediate class between First and Third (which later became Second).  The original Second was more or less abolished in the 1870s (as a result of the Railway Regulation Act 1844), remaining only in limited use for special services, such as those meeting ships (which retained the three-class system from which railway classifications had originated).  In the 1980s, BR renamed Second to Standard.  Many of the classifications listed below are no longer used, and some did not survive until the designation "Standard".