This article is from Tom Kirby, guide for the the American Alpine Institute, (AAI)
Not all “knots” are true knots. Technically, a true knot is capable of holding its form on its own without another object such as a post, eye-bolt, or another rope to anchor it.
Example: Figure 8 on a bight:
A hitch, by contrast, must be tied around something to hold together; remove the thing it’s tied to, and a hitch falls apart.
Example: clove hitch. Unclip this from the biner, and you don't have a knot at all.
A bend is a knot used to join two rope ends.
Example: flat overhand bend (formerly known as the "EDK", or "European Death Knot"):
In practice, we use “knot” as an umbrella term to cover all these types, but the distinction is useful to know.
If the context makes it unclear what you mean, you can use the term “hard knot” to distinguish a true knot from a hitch or bend.