People usually don't think about Perl's type system. Some would even mistakenly claim it doesn't have one. It is, however, a most unusual one that doesn't really look like anything else.

What is a type anyway? And what is a type system? I'm not going to precisely define it here, that's for academics, but generally speaking a type is a fundamental property of a variable or value that determines what operations can and can not be done with it and what invariants it must hold. In a strong type system it is a stable trait: it can't change over the lifetime of the value/variable.

In some type systems containers are typed (such as C) and values really don't exist separate from containers. In other typed systems containers are typeless but values are typed (e.g. Python, Javascript, …). There are languages where both values and containers are typed (e.g. Java, C#), typically this means that the container constrains the values in it.

Contrary to what you might expect, Perl has the latter sort of typesystem, but with a twist.