I'd ask Alan Kay
its his term.
Quote: "I made up the term 'object-oriented', and I can tell you I didn't have C++ in mind" - Alan Kay, OOPSLA '97
He'd say it needs garbage collection.
He'd also add it should be more message oriented than function calling oriented. (See thread from last week or so).
Or read his paper on the OpenCroquet site (opencroquet.org).
Smalltalk is dangerous. It is a drug. My advice to you would be don't try it; it could ruin your life. Once you take the time to learn it (to REALLY learn it) you will see that there is nothing out there (yet) to touch it. Of course, like all drugs, how dangerous it is depends on your character. It may be that once you've got to this stage you'll find it difficult (if not impossible) to "go back" to other languages and, if you are forced to, you might become an embittered character constantly muttering ascerbic comments under your breath. Who knows, you may even have to quit the software industry altogether because nothing else lives up to your new expectations.
--AndyBower