I don't know what scalar means exactly, but I'm trying to see if I'm thinking about it correctly. Does scalar relate to arbitrariness where the type of data could be any type, or a system is not able to know what the data is in advance. 
The term "scalar" comes from linear algebra, where it is used to differentiate a single number from a vector or matrix.  The meaning in computing is similar.  It distinguishes a single value like an integer or float from a data structure like an array.  This distinction is very prominent in Perl, where the $ sigil (which resembles an 's') is used to denote a scalar variable and an @ sigil (which resembles an 'a') denotes an array.  It doesn't have anything to do with the type of the element itself.  It could be a number, character, string, or object.  What matters to be called a scalar is that there is one of them.