FT-i golf clubs are designed by Callaway and feature fusion technology and Complete Inertial Design. Fusion technology (FT) puts different materials together in each club head to enhance performance. The 'i' part of the name refers to Callaway's Complete Inertial Design process, where design elements such as center of gravity, moment of inertia, and face design are optimized.
It is actually FTi which stands for Fusion Technology Iron. It is a hybrid product that combines the best of current technology to give you more power.