A titanium handle is machined from titanium alloy, most often 6AL4V. It is lighter than steel, does not corrode, and it is the standard material for frame locks because it has the spring characteristics the lock needs.
Titanium can flex repeatedly and return to shape, which is exactly what a lock bar has to do for the life of the knife. Steel can do it too but weighs considerably more for the same section.
Because titanium galls against steel, quality frame locks fit a hardened steel insert at the point where the lock bar contacts the blade tang. A titanium lock face with no insert will wear faster.
It is cold to hold in winter and slippery when polished, though bead-blasted and milled finishes grip well. It does not rust, and it scratches easily but the scratches blend into the finish rather than showing as bright metal.
Anodizing titanium produces color through an oxide layer rather than paint, so the color cannot chip off, though it can be scratched through.