NFC stands for Near Field Communication. It's the same sort of tech used for many card entry systems at buildings. Does your phone support Apple Pay or Google Pay? Then you've got it!
The NFC tag/light combo above brings up a URL. The light blinks then will go steady when the tag is read.
So, what sort of information can you embed on a tag? All sorts of cool things. A URL. Your social media page. A link to an image, file, or location on a map. Your contact information for someone to save to their phone. Your "In Case of Emergency" info.
People are using NFC tags on pet collars to hold owner contact information. The pet may be chipped, but reading it requires a trip to the vet. A compatible phone can read the data and perhaps reunite the pet with the owner a bit sooner. (This does not replace a chip, though as collars can be torn off.)
Now that you know what a tag is, you'll want to know if your phone supports it and how to program it. Please go to the tutorial
for all that goodness!