Ann Althouse had an op-ed piece in the Wall Street Journal last week attempting to deconstruct the notion of "activist" judges. In a fairly standard recitation of what lawyers of Ann's vintage (and mine) were taught, she says, essentially, that an activist judge is one that you disagree with. She points out that if, to use the ur-activist case, Roe v. Wade were to be overruled, there would still be litigation over things like the territorial reach of statutes that make abortion a crime, etc.
It's an interesting piece and I agree that the term judicial activism is, in and of itself, a conclusion rather than a description. Assuming that you regard judicial activism as a pejorative term suggesting that a judge has somehow overreached, you need to explain what you think judges ought to be doing and just what they need to refrain from doing.
Where I depart from Professor Althouse is in her suggestion that this is an impossible task; that there is, as she puts it, "no exit" from judicial activism.
Judicial activism, in my view, is not synonymous with judges deciding cases. Rather, it refers to judges deciding them on the wrong basis. Judges are supposed to be - in some sense - above the political fray (federal judges are, in fact, appointed for life) and we generally believe that they ought to be ruling on the basis of some source of authority other than their own personal views of what is and is not a good idea. Generally that source of authority is a legal text upon which authority has been conferred by, for example, passage by Congress or adoption by the people as part of their Constitution.
The meaning may be indeterminate. Interpretation may require resort to the type of tools of construction that lawyers typically use and, even then, reasonable people may differ as to the proper outcome. But what counts is interpretation of the text, not the judge's individual policy preferences. Using the term in this way, the outcome of Brown v. Bd. of Education (as opposed, perhaps, to its reasoning) was not an activist decision. The constitutional text clearly mandates equal protection and does so in a context that makes it quite clear that it is concerned with racial distinctions. Roe v. Wade is an "activist" decision in that the "right of privacy" on which it is based is not fairly rooted in any constitutional text and is incapable of definition by resort to anything other than the personal preferences of whomever is defining it.
This view is not completely immune from criticism. Some people argue that texts are so malleable that they answer few interesting questions. I don't agree. To say that words can mean more than one thing is not to say that they can mean anything