Apex rule refers to a principle of corporate law that an officer at the apex of the corporate hierarchy cannot be deposed unless the employee has special or unique knowledge, or the information is first pursued by less intrusive means.
The rationale behind the rule is that an apex corporate officer, like a high-ranking government official, often has no particularized or specialized knowledge of day-to-day operations or of particular factual scenarios that lead to litigation, and has far-reaching and comprehensive employment duties that require a significant time commitment. Therefore, to allow depositions of high-ranking government officials or corporate officers without any restriction or preconditions could result in the abuse of the discovery process and harassment of the parties. [Lilia Alberto v. Toyota Motor Corp., 2010 Mich. App. LEXIS 1501, 13-14 (Mich. Ct. App. Aug. 5, 2010)]
Apex rule also refers to principle of mining law that a vein of ore may be mined if it extends beyond the vertical boundaries of the surface claim on which the vein apexes.