The FaceRec app takes a picture of an individual and then compares it with a database of previously identified people. The application indicates the person's name as well as other potentially useful details such as their age, profession, etc.
The application is by no means authorised by Google, which has spoken out against programs that, like this one, could potentially lead to an invasion of privacy. Not having been validated by Google, FaceRec is available only on Lambda Labs' website, so Google Glass Explorers interested in trying it out have to download it there manually.