A homologous series is a series of compunds in which one compound differs from a preceding one by a - CH_{2} - group. Members of the homologous series are called homologs.
Characterisitcs of homologous series:
- Each homologous series is represented by a general formula. For example alkane series has a general formula C_{n}H_{2n+2}
- Members of a homologous series have similar chemical properties
- The physical properites change through out the series in a regular way. For example, melting points and boiling points increase in the series from methane to decane
- Members of the same homologous series can be prepared by the general methods of preparation.

https://en.wikipedia.org/wiki/Homologous_series