Management Job Titles

Hi,
I am struggling with differentiating between managment titles like "Head of", "Director" or "Manager" (are there more?).
Is there a clear hierarchy? Do these titles reflect duties and responsibilities somehow (budgets, strategic input etc.)?
Cheers,
Eric
Job titles at any level are just words - the actual definition of the job will be defined in the persons job description and vary from company to company.
Some words like "Director" can (but don't always) have a specific legal meaning in some places but most are just titles to be assigned as the company sees fit.
Titles are often given instead of raises, to reward studio staff.
Titles are sometimes given for business reasons, in order to open doors to meetings with other studios, publishers, etc; for example, a "Director of X" at a publisher might prefer to meet with a "Director of X" at a studio, instead of with a "Lead X" at the studio, even though there might be no difference between what a Lead does and what a Director does at that studio.
There is no fixed relationship in the industry between those titles, other than, if a studio has leads, managers, and directors, the positions have in my experience increases in responsibility in that order.
Serotonin's answer is excellent.
Another piece of absurdity is that in some companies, everyone's a Manager. I recall working with one smaller US publisher, where there were two people in a particular department - the woman who did the brainwork, and her assistant. Of course, their job titles weren't X "Executive" and X "Assistant" as you might expect - they were "Vice President" of X, and X "Manager".
So, sometimes the "Manager", or even "Director", is just "the only person in the company doing that job". You get it with small developers sometimes: "So, when you say you're the Art Director... you're actually the only artist, aren't you?"
I have experienced that sort of management structure (or rather lack of structure) over the years and it can cripple a company. It is especially common in small developers when none of the founders have previous management experience. They believe that as founders they all need to be managers/directors. The result is multiple people with overlapping management responsibilities or worse yet undefined responsibilities, which result in everyone wanting to be involved in every decision, even if it isn't within their field of expertise. Did a rather tongue in cheek post about this some time ago http://www.obscure.co.uk/blog/2009/03/18/steve-snowy-white-and-the-seven-directors/

Thanks for the answers so far. I'm not a native english speaker, so this could be part of the "struggle".
If I understand you correctly then there is no real difference between "Head", "Director" and "Manager" in a shallow hierarchy. Should several levels of hierarchy be required then the order would be "Head", "Manager", "Director". And these title do not carry any implied meaning relating to rights and duties.
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What is the nature of this struggle? Clearly you know that they are spelled differently. What is this "struggle" you are having?
And why are you having this struggle? If we knew the reason for your question, we could better give you the answer you are seeking.