An atom or an atomic value denotes a single element -- a number, text string, a handle, a reference, or the value Null, i.e. not an array (table).
A scalar is simply a single atomic number -- that is not an array.
Atomic values form the cells of arrays but they may also stand by themselves as values, e.g. the result of evaluating 1+2 is the atomic value 3, which is not an array. The Title attribute of any object is an atomic text value.
Because an atom can be seen as a zero-dimensional array, an atoms is functionally equivalent to an array with no indexes. In standard usage the term atom or atomic value is used to distinguish a simple value from an array or list (one-dimensional array).
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