You can call them smart tags, info tags or, in this case, NFC tags, but their basic architecture is similar to RFID tags. They both have a bit of storage memory, along with a radio chip attached to an antenna.
The only real difference is that NFC tags are formatted to be used with NFC systems. And they're small and cheap enough to integrate into all sorts of products: posters promoting circus tour dates, ski lift passes, stickers, business cards, prescription bottles and even ruggedized labels meant for outdoor use.
NFC tags are passive, meaning they don't have any power source. Instead, they literally draw power from the device that reads them, thanks to magnetic induction. When a reader gets close enough to a tag, it energizes it and transfer data from that tag. You can read more about magnetic induction in How Wireless Power Works.
There are four flavors of NFC tags, types 1 through type 4, all featuring different capacities and data transfer speeds. Type 1 tags typically store 96 bytes and work at 106 Kbps (kilobits per second); Type 4, the biggest and fastest, store up to 32 KB and work at speeds of up to 424 Kbps [source: Radio Electronics].
Anyone can buy blank NFC tags and then write customized data to them. Type 1 and Type 2 tags can be written to multiple times. These tags can also be permanently locked, or encrypted, so that no one can manipulate the data. Type 3 and Type 4 tags can only be written to once, like a CD or a DVD, and they lack the security of types 1 and 2.
Tags with higher memory and larger antennas are bigger in physical size. Generally, tag size ranges from just a centimeter or two to a few inches.
Memory capacity and speed dictate cost, which is a critical consideration for companies that want to spread information far and wide through smart posters or flyers. Right now, tags cost around 30 cents apiece even in bulk, but the price should continue to drop until they're only a few pennies each [source: NFC Rumors], allowing for rapid dissemination of these tags in innumerable places and things.
Soon, it's likely that NFC tags will be just about everywhere, letting you tap your way across your newly digitized world. If you want to know more about the coming new NFC world order, check out How Near Field Communication Works. You'll be better prepared to handle the onslaught of your NFC-enabled neighborhood and ready to rock out with your NFC smartphone.