A brand of memory card that includes Wi-Fi capability so that you can transfer photos wirelessly to a smartphone, tablet or computer. More and more cameras are coming out with Wi-Fi built in now, though, so these provide the same functionality as Eye-Fi cards.
Used rarely in digital cameras (except some cheap point and shoot models) but used extensively in external flashguns and battery grips. Alkaline AAs will do in an emergency, but rechargeable NiMH batteries are more cost effective and last longer between charges.
A direct cable connection between compatible cameras and printers that saves the trouble of transferring pictures to a computer first. It’s handy for quick prints and snaps, though most people would probably want to edit photos first or, these days, use online photo labs.