Is there a term to refer to languages where variables are not preassigned a type?

Question

For example JS, Python, Ruby, Smalltalk, etc. In those languages, the only place where the type of a variable is written in code is at instantiation time. I was thinking in the term 'loosely typed languages', but found it a bit, well, loose. References to papers that define nomenclature for this is also welcome.

Answer 1

It is usually called "Duck Typing". See https://en.wikipedia.org/wiki/Duck_typing .