The homologous series
Such a series contains substances with one type of functional group, with the same general formula and with similar properties.
Example: all alcohols have an OH group, a general formula CxHyOH.
But you have also ethers and esters etc. with the same idea.
The differences between members of a homologous series depend on the length of the carbon main chain CxHy.
Then methanol will evaporate much easier than propanol. But chemically they show lots of similar reactions.