There are several hidden villages, which are supposed to be hidden (it is all in the name..!) But, everyone (at least everyone who matters) seem to know where these hidden villages are. Or, are at least able to easily find out where they are.
So, why are they called hidden villages? Is it more a 'title' or 'status' for these villages?
The literal translation for Konohagakure no Sato is "Village hidden in the leaves" (not hidden leaf village). Here hidden is used in the sense of "surrounded by" or "enclosed by". It does not mean those places are literally hidden from the world. It is similar for other villages, such as Amegakure no Sato (village hidden in the rain), Sunagakure no Sato (village hidden in the sand), etc.
They are not literally hidden. The villages are there to serve their country and it's landlord, to protect them from enemies and to perform various missions.
The ninjas are not seen standing on every corner, yet they are a considerable force that can defend the country, or act as spies. It's somewhat like an Intelligence agency in real life. You know they exist, you know where their headquarters are, but they perform some "hidden" activity which can't be easily spotted by common people, yet is very important for the country.
The villages are all independent and each has its own secrets, hidden techniques, et cetera, which they guard from other villages. The locations of each village although not completely a secret are obscured, preventing them plans or other sensitive information from leaking out.
The villages were probably truly hidden when they were established, but over time became more well known (the are the centers of economy for each country). Villages need commissions to stay afloat. They probably can't get many commissions if they are hard to find.
Calling them "hidden" is most likely a reference to real life ninjas that lives in hidden villages, remote settlements for ninja in Japan during its Feudal period. It also gives the villages a certain mystique.
