Homologous series: A homologous series is a series of organic compounds that have the same functional group and similar chemical properties, with each successive member differing by a CH2 unit.
Isomer: Isomers are compounds that have the same molecular formula but different structural arrangements of atoms, leading to different chemical and physical properties. There are different types of isomers, including structural isomers, geometric isomers, and optical isomers.