Literally: one – mouth – both – tongues
Alternately: Saying one thing and then saying something incompatible later on. Equivocating or, more often, outright lying depending on what’s convenient to say at the time. Speaking with two tongues. Acting presidential, ha ha ha.
Notes: A variant of the compound bumps up the number of tongues to three: 一口三舌 (i-.kkou.san.zetsu).