Loft
The angle of the clubface relative to a vertical plane, which controls launch angle and, largely, distance.
More loft (like a wedge) sends the ball higher and shorter; less loft (like a driver) sends it lower and further.
See the related guide: When is it worth getting fitted?
A full explanation, in plain language.
More equipment terms
Lie Angle
The angle between the shaft and the ground when the club is soled correctly at address.
Bounce
The angle built into the sole of a wedge that helps it glide through sand or turf instead of digging in.
Offset
A design feature where the leading edge of the clubhead sits slightly behind the hosel.
Shaft Flex
How much a shaft bends during the swing, rated from Extra Stiff down to Ladies/Senior flex.
Cavity Back vs. Blade
Two iron head designs: cavity-back irons hollow out the back of the head for forgiveness, while blades (muscle backs) are more compact for feel and control.
Hosel
The part of the clubhead that connects to the shaft, the exact spot a shank makes contact with instead of the face.