An array is an array of anything. A string is a specific kind of an array with a well-known convention to determine its length.
There are two kinds of programming languages: those in which a string is just an array of characters, and those in which it’s a special type. In C, a string is just an array of characters (type char), with one wrinkle: a C string always ends with a NUL character.
The “value” of an array is the same as the address of (or a pointer to) the first element; so, frequently, a C string and a pointer to char are used to mean the same thing.
An array can be any length. If it’s passed to a function, there’s no way the function can tell how long the array is supposed to be, unless some convention is used. The convention for strings is NUL termination; the last character is an ASCII NUL (‘’) character.