NFC (Near Field Communication) is a relatively new standard that lets you bump your phone against a sensor (or another phone) to share information or make a payment. Although it's widely used in Asia and some European countries, the technology isn't very widespread in the US – only a few phones stateside sport the technology, and payment sensors are still few and far between.
NFC-enabled phones, such as the Samsung Galaxy Nexus and Galaxy S II and the LG Optimus LTE, can share videos, websites, and apps with each other wirelessly (by bumping two phones together) or pay for things using Google Wallet or the forthcoming ISIS system.
If you don't have an NFC-enabled phone, don't fear – an app called Bump lets you share photos and info between phones in pretty much the same way. Bump can be a little flaky sometimes, and it doesn't support wireless payments, but the upshot is that it's cross-platform, so you can share things with your iPhone buddies, too.