What is a homologous series? Explain with an example.

(N/A) homologous series is a group of organic compounds that have the same functional group and similar chemical properties,and in which successive members differ by a $-CH_2$ unit.
For example,the alkane series is a homologous series with the general formula $C_nH_{2n+2}$.
$1$. Methane: $CH_4$
$2$. Ethane: $C_2H_6$ (or $CH_3CH_3$)
$3$. Propane: $C_3H_8$ (or $CH_3CH_2CH_3$)
$4$. Butane: $C_4H_{10}$ (or $CH_3CH_2CH_2CH_3$)
In this series,each successive member differs by a $-CH_2$ group,which corresponds to a molecular mass difference of $14 \ u$.