‘Multipad’ is a catch-all term for pads that include multiple functions and quite literally: multiple pads. Each multipad will have different qualities and functions; for example the Alesis Strike MultiPad has a large library as well as 32GB of space for uploading your own samples.
The Yamaha DTX Multi-12 does not offer anywhere near that much space, but it supports finger and hand drumming, with mutable pads, meaning it feels much more realistic to play. Then you’ve got the Nord Drum 3P - also filed under ‘multipad’ - which is a drum synthesizer.
Ultimately, there are pads out there to suit a whole host of different needs, so it’s important to be clear on what specific role it will play within your music creation.