It is a machine readable passport that in addition to personal data and fingerprints of the holder, has a micro chip where a digital facial image is registered.  It also has a unique ID number and digital signature which prevents counterfeiting.

These passports are being used in Spain since 2007.  It is each passengers responsibility to ensure that their destination accepts old or new Biometric passports.

Some countries like the USA and Dubai ask for mandatory Biometric passports.

to confirm which documentation is necessary to take your flight you must consult the appropiate Embassy in question.  It is the passengers sole responsibility to carry the correct documentation, bearing in mind the destination and any connections.