what is the meaning of hydrates of carbon ?

In classification it's written that they are broadly classified on basis of products formed on hydrolysis....What is being hydrolysed here ?

carbon is being hydrolysed. but despite it being said that carbohydrates are hydrates of carbon, it is not completely true. this type of classification was made during times when science was not advanced enough since c(h2o) is also of the form of a mono hydrate of carbon but this is not a formula of a carbohydrate but of formaldehyde. also rhamnose is such a carbohydrate which has the formula (C₆H₁₂O₅ ) not in the format of being a hydrate.

hope this helps!