It all depends on how technical you want to be.
(I am writing as the spouse of a nationally recognized expert on wild turtles, tortoises and terrapins in the US.)
In the US there are 50 species of "chelonians" excluding sea turtles. Among experts they are identified by strict Latin taxonimic names when precise species identification is required. There is also a looser English taxonomy, but there is enough regional variation that experts fall back on Latin when confusion arises.
But, even experts in "casual" conversation use the word "turtle" to include "turtles, tortoises and terrapins"; e.g. "I study turtles."
Some non-experts refer to the shelled animals that live primarily in water (lakes, rivers and streams) as "turtles" and those that live primarily on land as "tortoises". However, in the US northeast, the most common land dweller is the "box turtle".
Bottom line, in casual conversations in the US the word "turtle" encompasses all those shelled creatures.
In discussion with passionate "turtle people" try to use the correct taxonomic name.