What does the word Hydrate mean in terms of carbohydrate?

The word hydrate in the chemical name of a compound normally means that
the compound has water molecules in the compound molecular structure. That
is not the case in Carbohydrates.
A Carbohydrate is an organic compound with the empirical formula CxH2nOn.
The ratio of H to O is that of water, but that does not mean there are actually
water molecules in them.
Carbohydrates are polyhydroxy aldehydes, polyhydroxy ketones or compounds
that can be hydrolyzed to them.
Examples of carbohydrates are: glucose, sucrose, lactose, starch, cellulose.