I feel like my reference point should be Dilbert. :)
I'd suspect Urban Dictionary is a decent source, too, but the micromanaging company web filters here won't let me see it. Ironic, no?
Here's my working definition based on personal experience:
Micromanagement is, to an extent, in the eye of the beholder. While there may be a lower bar that is established by a team, corporate culture, national culture or career domain at large, in general Micromanagement is providing task direction in such small, overly specific, focused statements that the person receiving the micromanagement is unable to contribute meaningfully to the work at hand or take any pride in having accomplished anything.
What I find intersting, personally, is that micromanagement can largely be a matter of personal experience. For example, here's some cases:
Explaining to the new intern exactly how we perform a build (and more importantly why) is not micromanagement the first time. Explaining to the new intern how to perform a build every time IS micromanagement.
Explaining some particular crucial success or failure details of a feature development assignment to a mid-level engineer who doesn't have a history of good judgement or good colllaboration practices is not micromanagement. Explaining these same details to a star engineer who always does a great job of checking in and working out sellable details with sales engineering IS micromanagement.
Dividing up and prioritizing features for development and parceling them out to engineers is NOT micromanagement when you are the task manager for the team. It IS micromanagement when you are that task manager's manager.
A general good rule of thumb is, if you are essentially making all the decisions of the person one level down from you, you are probably micromanaging. Conversely, if you are coaxing, arguing or selling a contratry idea to the person one level below you, you are not micromanaging. But there is sometimes a profound gap between the manager things he is doing (aka, "convincing") and what the employee things is happening (aka, "dictating). Especially in a knowledge based career - we pay people for their good judgment and visionary work. When we take away any ability to make judgement calls or contribute to the vision, we are not only micromanaging, we are wasting the value of the employee.