Rapid Voice Cloning is a quick process of creating a voice model in minutes, typically used for fast prototyping or testing. Custom Voice, on the other hand, involves creating a more refined and tailored AI-generated voice model for a specific brand or project, ensuring a unique and consistent vocal identity. Rapid Voice Cloning only requires a few seconds of training data and is available at all times to all users at no cost, while a full Custom Voice requires significantly more data.