Noob question: what does "backed" mean in this case. That you can always exchange your $1 ecash for $1 of bitcoin at the mint? 

 Yes, exactly. There are several ways to achieve this:

- Stablesats [1]
- DLCs [2]
- Stablechannels [3]

[1] https://stablesats.com/
[2] https://10101.finance/
[3] https://github.com/toneloc/stable-channels