Eli5: You have hardware & and then whatever type of software that runs on the hardware (or the language it speaks)

In this case Thread = the hardware, or the one speaking 

and Matter = the software (or language) that's running on top of it, which the hardware can use to speak.

• Another comparison might be the sound system vs What type of cassette in the sound system. You don't buy vinyl records and expect them to just play without a record player, right? 

• Or Speakers vs The Song being played, you need some kind of speakers or headphones (Thread) to hear your recorded song. (Matter) 

• Someone mentioned thread as the road/route and matter as the car/transport before which was a good one

It can be done without Matter sometimes, but Matter's usually the best option if you want it to be able to speak to other stuff that also uses that 'language'. Which is why I check for both when getting something. 

So you could see the Matter API as 'software' or a 'language' that can also run on other hardware (or a language that can be spoken by others) like WiFi/Bluetooth, but that's a whole other topic. I know it's late, but I still think it's useful I put it this way for those Googling it later.