This is something only slightly stronger than monotonicity. I think that in category theory this would be a fully faithful functor, but I'mI’m not sure if there is a standard name for this in order theory.
For context, I'mI’m working in a theorem prover (Isabelle) and this is a property of the function which converts words to natural numbers (embedding {$0 \ldots 2^{32} - 1$}$\{0 \ldots 2^{32} - 1\}$ into $\mathbb{N}$).