Types, loosely defined, are about capabilities. What are the capabilities available on a value of a certain type? Programmers experienced with strong and statically typed languages will probably have a more visceral appreciation of this, but even programmers of weakly and dynamically typed languages like JavaScript, encounter the reality of types and their capabilities; only that they do so at runtime.
For example, a JavaScript developer might type out the following code:
> "3".toExponential()
But this will fail at runtime because the "3" is of the String type and it does not have the capability to be shown as exponential. The following, on the other hand, will work seamlessly:
> (3).toExponential()
'3e+0'
Because 3 is of the number type and the number type has the capability to be formatted in exponential form.
Rust extends the idea of types to now include capabilities that relate to memory management. These capabilities ensure memory safety in Rust.