In Linnaeus' time, people already talked about species.

A species is sort of plant or animal all of the same type, like 'horses' or like 'goldfish'.

People also already talked about groups of animals that were similar -

like {horses and donkeys and zebras}, or like {carp and goldfish}.

They called a group a genus. Lots of groups aren't called 'genuses', but genera.

They didn't have any system for grouping genera together.

It was rather like having books grouped into {books on trains},

but no group for {Transport} or for {Non-fiction} or for {Children's Books}.

Linnaeus started with species and grouped them into genera.

He then grouped genera into orders. Orders were grouped into classes

and classes were grouped into kingdoms.