What does it mean when an iPhone has an undefined carrier? Does it mean it’s unlocked?

[Low Key1]

The phone has a unlocked esn the fmi is off and it says carrier undefined

 

[Just_Me_D]

I’m not sure, but I would guess that the device is probably unlocked and not tied to a specific carrier. Again, I’m only guessing.

 

[TwitchyPuppy]

The phone has a unlocked esn the fmi is off and it says carrier undefined

Where does it say carrier undefined?
And “unlocked esn”, my guess would be that the phone is unlocked and carrier undefined is probably because it’s never been activated before.