tristate

[trahy-steyt] /ˈtraɪˌsteɪt/
adjective
1.
pertaining to a territory made up of three adjoining states:
a tristate league.
2.
pertaining to the three adjoining parts of such states:
the tristate region of Missouri, Kansas, and Nebraska.
Also, tri-state.
Origin
British Dictionary definitions for tri-state

tristate

/ˈtraɪˌsteɪt/
adjective
1.
(of a digital computer chip) having high, low, and floating output states