Metavirus says:

your formulation of judicial activism is too simplistic. of course Brown and Lawrence and Roe were judicial activism. the problem with the term in modern times is that people on one side are unwilling to recognize that some decisions that go their way are also judicial activism. The technical (non-partisan) definition of judicial activism is generally when a court ignores prior precedent and, especially, the will of the people expressed through their representatives in Congress and creates new policy (i.e., "law" when the Supremes do it)

Here's a good summary from Wikipedia:

"Judicial activism" is frequently used in political debate without a clear definition, which has created some confusion over its precise meaning.

Bradley Canon posited six dimensions along which judge courts may be perceived as activist:

* Majoritarianism — This dimension takes into account the degree to which policies adopted through the democratic process are judicially overturned.
* Interpretive stability — This dimension takes into account the degree to which court decisions alter earlier decisions, doctrines, or constitutional interpretations.
* Interpretive fidelity — This dimension takes into account the degree to which constitutional provisions are interpreted contrary to the clear intentions of their drafters, or the clear implications of the language used in the provision. (See also Judicial interpretation)
* Substance/democratic process — This dimension takes into account the degree to which judicial decisions make substantive policy, as opposed to acting to preserve the democratic political process.
* Specificity of policy — This dimension takes into account the degree to which a judicial decision establishes policy itself, as opposed to leaving discretion to other agencies.
* Availability of an alternate policymaker — This dimension takes into account the degree to which a judicial decision supersedes or inhibits serious consideration of the same problem by other government agencies.[1]