Not where I come from, it's Electronic Countermeasures. Actually I think the term used by Toyota is Electronic Control Module since the Prius is just a computer that burns gas and there are ECM's in everything. Not just engine control.
In Toyota’s English-language service documentation (more info), the generic term is ECU, Electronic Control Unit; the ECM, Engine Control Module, is the ECU for the engine.
Unlike some other automakers, Toyota doesn’t impose a per-vehicle charge for updated ECU software, and most of the updates can be downloaded from techinfo.toyota.com with a Professional Diagnostic subscription, from $65. If you’re considering a do-it-yourself update, be sure to read and follow T-SB-0134-16 Rev1, “Techstream ECU Flash Reprogramming Procedure” (PDF). For updates installed by Toyota dealers, the cost, if any, depends on the reason for the update. Safety recalls, such as the update for the Power Management Control ECU in recall J0V, are done at no charge to the owner. The same is usually true for service campaigns, at least until the campaign expiration date, if any. Updates announced only in technical service bulletins, such as the ECM update in T-SB-0103-12, “MIL ‘ON’ DTC P2111 and P0A0F After Cold Soak,” generally don’t have any special coverage, beyond the warranties included with the new vehicle. If the parts involved are still covered, the update is a no-charge warranty repair; after the warranty ends, the owner would have to pay for the dealer’s labor. Keep in mind that these updates usually apply only to vehicles that have the specific problem described in the service bulletin.
