I was reading about multiple jobs in the industry and I was reading about the toolbox items. I didn't understand what is the difference between duct tape and gaffer tape. Can anyone please explain? 

You can use Duct Tape for anything you need. The only problem is the stickyness. When you remove it, there is a lot of glue residue on whatever you applied it on. When you are working with expensive gear, you don't want that. So you use Gaffer Tape. It does the same thing as the Duct Tape except it leaves less glue residue on the equipment.

You use gaffer tape because it has less glue and it's less sticky than the normal one. You wish to remove the tape when you're done. You rarely want to remove the other type of tape.