What is a land loan, is it different than a mortgage, and how?

From what I understand, a mortgage is a loan secured by real estate. Thus under this definition you should also be able to buy land (secured by the land). Is this true? If it is how come there are stuff called land loans? Do they also technically count as mortgages? Also, this definition doesn’t specify what you can do with the amount loaned out, can you buy whatever you want as long as you have some sort of real estate property as collateral (in terms of a technical sense, I’m not asking if this is practically possible)