A steward is a single person who speaks for a resource that cannot speak for itself. He or she is responsible for the best interests of that resource, and is an advocate and champion for that resource. A steward specifically is not a committee or governing body, although one may be formed to support and advise the steward if the resource is especially large or important.
For example, one might be the watershed steward for a watercourse. It would be your responsibility to speak on behalf of the watershed whenever decisions potentially impacting that watershed are being made. You must in some way become the watercourse -- to live its life, imagine its social interactions, know what would cause damage.
From the sublime to the trivial, one might be steward of a book. Your name would be on the book, and you'd know who had borrowed it -- and more importantly, the borrower would know that someone's job is to look after the book; it is not simply a common resource, shared by many, cared-for by none.
And from the trivial to the abstruse, the Kingdom of Bhutan has a Minister of Happiness, whose duty is to see that the best interest of happiness is served in the Kingdom. (Western nations have Gross Domestic Product, Bhutan measures Gross Domestic Happiness.)
Stewardship is subtly different than ownership in a number of ways. For example, one may "own" something, like a beater car, that one has no interest in maintaining, but rather will drive it until it falls apart. Or one may "own" an investment, like shares of stock in a public company, in which one has no maintenance interest, only an income or value growth interest.
Contrast this with fulfilling the responsability of stewardship. One might choose a longer-lived vehicle, rather than letting a cheaper one fall apart. Or one might attend shareholder meetings to see to it that the company was properly cared for, rather than simply collecting dividends and trusting the corporate board -- who often turn out to be a pack of theives.
A subset of stewards is chosen by consensus from the general membership to serve as association directors. Ideally, every member will be a steward/director of the association, subject to residency requirements in our association rules.
Everyone is a steward
In some cases, as in the Minister of Happiness or even "watershed steward", the steward may have considerable influence over many people's lives. In the case of a book, it is tempting to say, "Why bother?" But it is important to note that each one of us will hold multiple, simultaneous stewardship roles, and that the sum influence of a person who cares for many minor resources may be as great or greater than that of the person with one major responsibility.
Most of us can agree that individual property ownership has failed mankind. Many of us can look to the ruins of state-imposed Communism to see that common property ownership has also failed. It's time for a new model of resource management.