People administering computers professionally, as part of their job.
I think these definitions only roughly describe the site concept. For example, somebody working as professional system administrator by a non-profit, non-governmental organization still qualifies the site topic, although it doesn't pass the strictly interpreted "business environment" criteria.
But, for example, a non-technical leader of an IT department of a big company still "manages IT systems in a business environment", despite that his focus of interest and the site topic are probably distinct.
But these are rare exceptions. If we see the idea, the vision of the site, the definition is to me okay.
You can find more proper definitions in the site tour, and on this meta site.
In concrete cases, the vote of the 3k+ users decides about the questions, they are following mainly the idealistic description with different levels of strictness.