Communicate: State i and j communicate () if i is reachable from j and j is reachable from i. (Note: a state i always communicates with iteself)

Irreducible: a Markov chains is irreducible if all states are in the same communication class.

Absorbing state:

Closed Set: a set of states S is a closed set if no state outside of S is reachable from any state in S. (This is like absorbing set of states)

: be the probability that, starting in state i, the process returns (at some point) to the sate i

Transient: a state is transient if

Recurrent: a state that is not transient is recurrent, i.e., . There are two types of reurrent states

Positive recurrent: if the expected time to return to the state if finite

Null recurrent: if the expected time to return to the sate i is infinite (this requires an infinite number of states)

Periodic: a state is i period if where k is the smallest number such that all paths leading from state i back to state i has a multiple of k transitions

Aperiodic: if it has period k =1

Ergodic: a state is ergodic if it is positive recurrent and aperiodic.