In organic compounds, there exists a series or a group of compounds having the same functional group and similar chemical properties in which each succeeding compound differs from the preceding by -CH2 group or 14 molecular weights. Such a series is known as the homologous series. 

In other words, homologous series is defined as a series of organic compounds in which all the organic compounds can be represented by the same general formula and each successive homologue differs from the preceding by a -CH2 group or 16 molecular weight.