MOI stands for Moment of Inertia. It basically means how resistant something is to twisting or rotating. In golf terms MOI refers to how much a clubhead or putter head resists twisting on off – center hits.
A High MOI driver / putter means more stable, less twisting.
A Low MOI twists more which is less forgiving on off – center hits.
What it means for the golfer – A higher MOI club is generally more forgiving, and helps the ball go straighter when you miss the sweet spot. That is why you hear about ” 10K MOI ” drivers right now – they’re designed to be super stable. The same principle applies to putters which is why you see so many tour players now using High MOI mallet style putters.