What are aromatic and aliphatic compounds?

Hint: Generally two types of compounds are present alkyl and aryl groups where alkyl are those groups which have a chain like structures whereas aryl are those which contain rings in their compound structure.

Complete answer:
An aryl group can be defined as a functional group attached with ring-like structures and that structure or substance is known as the aromatic compound or aromatic ring-like compound. Generally the aromatic ring is a hydrocarbon in nature. The compounds containing aryl groups are known as aromatic substances and those who have only alkyl groups present in them i.e. there is no ring present in that compound then that is known as aliphatic compounds.
Due to the hydrocarbon nature in aromatic compounds they have suffix -yl for example thienyl, phenyl, etc. The process of attaching an aryl group to a substituent is called arylation. Arylation is done by the reactions which come under the cross coupling reaction types. Whereas aliphatic compounds are single chain like compounds which contain branches or may be saturated or unsaturated in nature.
Hence from the above discussion we can conclude that aromatic substances are those which have rings present in them and aliphatic are those which do not contain any ring.

Note:
The main example of aromatic substance is phenol in which $OH$ group is present along with benzene ring and aliphatic substances may be alkane, alkene or alkyne in nature the main examples are n-propane, butane, butyne etc.