What does alkyl mean?
Removal of a hydrogen atom from the alkane molecule gives alkyl molecule.
Normally one of the functional group of the alkanes.
The general formula for an alkyl molecule(acyclic):-
where n= no.of carbon molecules.
On removing one hydrogen molecule we get,
A functional group based on alkanes.
An alkane minus a hydrogen atom which is attached to another molecule and thereby becomes a functional group is an "alkyl group".
So for example, if the alkane is ethane