Bisimulation from Wikipedia

Bisimulation - Wikipedia
Bisimulation

In theoretical computer science a bisimulation is a binary relation between state transition systems, associating systems which behave in the same way in the sense that one system simulates the other and vice-versa.

Intuitively two systems are bisimilar if they match each other's moves. In this sense, each of the systems cannot be distinguished from the other by an observer.