That was the difficult question facing the court in Advanced Modular Sputtering, Inc. v. Superior Court (2005) 132 Cal.App.4th 826. An excerpt from the opening paragraph of the opinion gives you an idea of the substantive issues facing the court (emphasis added):
We hold that Code of Civil Procedure section 2019.210 (formerly Code of Civil Procedure section 2019, subdivision (d)), which provides that discovery relating to a trade secret may not commence until the trade secret is identified with “reasonable particularity,” is not limited in its application to a cause of action under the Uniform Trade Secrets Act (UTSA) (Civ. Code, §§ 3426-3426.11), for misappropriation of the trade secret, but extends to any cause of action which relates to the trade secret. We also hold that where the plaintiff makes a showing that is reasonable, i.e. fair, proper, just, rational, the trade secret has been described with “reasonable particularity,” and is sufficient to permit discovery to commence.
The italicized holding is about as specific as the court can get, because the trade secret designation was under seal. In footnote 2 of the opinion, the court states:
To avoid disclosure of the parties’ confidential information we are, in this publicly available opinion, purposefully vague in our descriptions of the claimed trade secrets, the trade secret designations, the expert witness declarations and other related documents.
The court comes up with a pretty good articulation of the standard for “reasonable particularity,” considering it is foreclosed from demonstrating specifically how the standard applies to the trade secrets before it.