Reptile & Amphibian Forums

I did a search of the forums but couldn't find the answer to this, so I apologize for those who have read the answer before.
I'm wondering what IS the difference between turtles and tortoises. I used to think it was the oversimplified difference between aquatic (turtle) vs. not (tortoise). But I don't think that's really the determining factor. I looked it up online and the only difference I came across was that supposedly turtles cannot retract their heads into their shells -- needless to say, I know that's not always true since box turtles are obviously capable of doing so.
Can someone please explain to me the distinguishing factors between the two? Or is there really no difference but in how we have decided to name one species vs. another?
Thank you very much.
-----
Edward
Carpe diem

This really is an open debate. It depends on what country you live in. Here the general idea is that a turtle spends at least a portion of it's time in the water and has some webbing between the toes. (even box turtles have very minute bit of webbing.) Tortoises are by and large terrestrial without webbing between the toes. I am pretty sure that this is the way we define them in the US but in other countries species that are fully aquatic are called tortoises.

I think in some other countries the word 'terrapin' comes in as a major player somehow. In the US I always heard that tortoises have 'elephant' feet and turtles have web feet.
At least it's better than the difference between 'frog' and 'toad', which is almost completely arbitrary.
-----
"The serpent crams itself with animal life that is often warm and vibrant, to prolong an existence in which we detect no joy and no emotion. It reveals the depth to which evolution can sink when it takes the downward path and strips animals to the irreducible minimum able to perpetuate a predatory life in its naked horror."
Alexander Skutch

In American English, the term turtle can be applied to any species in the order chelonia but is usually reserved for aquatic freshwater and purely marine turtles.

The term tortoise is reserved for the 50 species of mostly terrestrial based chelonians in the family testudinidae.

A terrapin is a brackish water or esturine chelonian (i.e. diamondback terrapin-Malaclemys, mangrove terrapin-Batagur, painted terrapin-Callagur).

Australia has no terrestrial chelonians, yet they call all of their freshwater turtles, tortoises.

The term tortoise is more freely used for all chelonians in many areas of the world outside of the U.S.

n/p
-----
Edward
Carpe diem