Which format is known as a multimedia messaging service?

The format known as a multimedia messaging service is MMS. MMS allows users to send messages that include multimedia content such as images, audio, and video, in addition to standard text. This capability significantly enhances the messaging experience by enabling richer communication. In contrast, SMS (Short Message Service) is limited to text-only messages, which restricts the type of media that can be shared.

iFrame is a technique used in web development to embed another document within a web page, and WEL is not a widely recognized term in the context of messaging formats. Therefore, MMS stands out as the correct answer because it specifically encompasses multimedia elements, which are essential to the definition of a multimedia messaging service.