I recently encountered a debate about whether Objectivism was the same as the philosophies of Ayn Rand. Wikipedia tells me they're synonyms. Is there another definition of "objectivism"? Has objectivism evolved beyond what Rand defined it as? What are the differences between pure, Randian Objectivism and other versions, if there are any?
"Objectivism" means a whole lot of different things.
It means the viewpoint that most people share that there is an objective reality that exists independent of human consciousness.
It also has a meaning in ethics, where objectivity usually is the view that moral judgments are objectively true or false.
And lastly it can be a reference to Ayn Rands philosophy, that amongst other things attempt to reach objective moral judgments from the assumption of an objective reality.
They are definitely not synonyms:
Objectivism as a branch of metaphysics and epistemology is a capacious topic that deals with the relationship between human perception/consciousness and the objective physical reality of the outside world. Like classical objectivism and unlike idealism, Randian objectivism assumes that the outside world exists, but also posits a moral framework which is usually described as "the morality of selfishness."
The term "Randian" is very much a slur in comparison to the term "Objectivist." Think of it like referring to the "Tea Party" people (or really anyone from the right) as "Teabaggers."
The perception is that Ayn Rand had the type of personality that did not accept disagreement among the people she associated herself with, and this was true to an extent. One application of the term "Randian" is essentially viewed as students of Objectivism who follow a person, as opposed to ascribing to a philosophy. Some people did (and do) treat Ayn Rand as if she's one of the romanticized perfect characters in her books.
The term "cult" is thrown around a lot, and maybe its applicable to some groups of Objectivists. There are a lot of different types of Objectivists you can meet. One particular strain most associated as a "Randian" are the hyper-judgmental, very insecure, socially awkward types. This is obviously a stereotype but some of them do exist in the same severity as the Westboro crowd.
The difference between the two isn't in philosophy. In fact I don't think there have been any major schisms on thought. It's not like when the Protestants split off from the Catholics. This is an unofficial label applied subjectively for a number of reasons (ignorance possibly being one of them) to Objectivists. Where most schisms occur is when one Objectivist comes to believe that the actions of another Objectivist are inconsistent with the principles of Objectivism.
Definitely take note of what the other answerers have provided, which are valid. Additionally, I would like to add that, if you refer to the Objectivism as Ayn Rand coined it, then "Objectivism" is, quite literally, "the philosophy of Ayn Rand." If you were to deviate from that philosophy, then you may still hold the premises of objective reality and the epistemology and ethics that follows, but form slightly different conclusions and no longer be an actual Objectivist.
I was heavily inspired by Rand and I have read a lot of her work. I have found myself in agreement with her concept of a reality in accordance with the Law of Identity; with reason as man's only valid source of knowledge; as life qua man as the essential principle of ethics; and as capitalism as the only political system commensurate with individualism, which is the most productive outlet for a social construct.
However, Rand also explored subjects such as sexual philosophy (animalistic behavior), psychology (man is born a blank slate), and physics (determinism and no random events in the Universe) -- the latter two of which is clearly the product of popular scientific theory at the time. The fact is, in any conflict between a philosophy and science, science is the victor, and the philosophy needs to be adjusted. But since Rand is dead, and whether or not she left the philosophy of Objectivism to the hands of her student Dr. Leonard Peikoff is debatable, I would say that, for certain purposes, deviating from the school of Objectivist philosophy is necessary.
In sum, Objectivism and Randian philosophy are both terms that describe the exact personal philosophy held by the author and philosopher Ayn Rand -- the former of which describes the actual philosophy, and the latter a more derogatory term (as another answerer pointed out, it's like calling a Tea Partier a "teabagger"). Neither of these terms may describe most people today who call themselves "Objectivists" -- because, if you are a pseudo-Objectivist who only picks and chooses which of Rand's ideas you follow, you aren't an Objectivist -- and if you truly understand the messages she tried to convey, you would also understand what I have described, and you would have adapted a modern stance of Objectivism and would no longer be the philosophy frozen in time at Rand's death.
The word "Objectivism" is a homonym, referring both to the broad philosophical position in favour of objectivity supported by various schools of philosophy, and also to the specific philosophy of Ayn Rand and related philosophers who follow her philosophy. Rand named her philosophical system "Objectivism", owing to the importance of objectivity in that system.** Since you are using the capitalised term, I am assuming you intend to refer to the latter.
Taking that as your meaning, whether or not there is a difference between "Objectivism" and Rand's philosophy and works depends on whether you view "Objectivism" as denoting only Rand's work, or whether you view it as a broader system that can be extended, modified, etc., by others. The Objectivists at ARI have generally taken the former view, while those at the Objectivist Center have taken the latter. On the latter view, Rand's philosophy forms the core of Objectivism, but the philosophy is broader than her work, and includes later extensions and refinements by others who have developed it further in later material.
Why is this controversial, and a cause for argument? I think it is fair to say that the Objectivists at ARI are concerned that people might end up modifying her philosophy in some essential way and calling their modified philosophy "Objectivism", which would be a misrepresentation. On the other hand, those who view it as a broader system as less worried about this, and are of the view that it is better to conceive of this term as encompassing the broad philosophical system, unconstrained by the limits of what Rand herself discovered.
(In regards to this issue, it is also worth noting that Objectivists tend not to use the word "Randian", and this term has generally been used by opponents as a sneer. Personally, I don't take that term to be inherently insulting; after all, we refer to Kantians, Aristotelians, etc. Nevertheless, it has been deployed in that way by critics of Objectivism, so it has come to be imbued with hostile intent.)
** Incidentally, Rand also noted in her work that she would have preferred to call her philosophy "Existentialism" (owing to the fact that its first foundational axiom is that existence exists), but that name had already been pre-empted by the Existentialist philosophers, with whom she had major differences.