'Central' stations are usually the main stations in a city with other railway stations. In most occasions, they are somewhat centrally located. But mostly, these are stations that come up as new terminals when the city already has other stations. This was not a universal thing though, and not all railway companies followed the same nomenclature. The Central stations that still survive, were just the 'major' stations in cities which took over from their original main stations (except MAQ).
Madras Central - Royapuram (RPM) was the initial terminus. MAS came up as RPM was too far to the North of the city and had some problems with freight traffic.
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TVC - The original terminus station in Trivandrum was between the present day KCVL and TVP stations in Chakai, which was the outskirts of the city back then. A more centrally located, larger terminus was constructed at Thampanoor a decade later and named as Trivandrum Central.
Bombay Central - The terminal station for the BB&CI railway was at Colaba ( present day BCT was only a passing station at Bellasis road) for more than 60 years. BCT was opened in 1930 as the new terminus and main railway station. In this case, it was just the main station and not related to it's geographical location.
Mangalore Central - This is very recent change. The Mangalore railway station was renamed to Mangalore Central in 2007 along with Kankanadi station which was renamed to Mangalore junction. Again this was just to indicate that MAQ is the main station for the city. This followed the Gauge conversion of the MAQ-Hassan line which made Mangalore a BG junction, leading to the renaming of the stations.
Kanpur Central - Similar to BCT. It wasn't a Central station until the 1930's, when the new station was constructed to handle the increased traffic and manage the combined BG and MG traffic.