Duct tape is the plastic/fabric stuff that comes several inches wide on big rolls. Gaffer tape has a different adhesive that doesn't get left behind, and is more expensive. The big DIY stores usually sell branded versions at huge prices - I usually get it from www.cpc.co.uk and keep a roll in the car.

Electrical tape doesn't stick to skin very well, but the adhesive in duct tape loves warmth (no jokes about hamsters!)

Gareth