I don’t quite understand what exactly WI-FI is (regarding to the computer network theory). There are many different definitions of this term. Somewhere it's written that it's a wireless LAN technology, somewhere it's a wireless LAN protocol, and somewhere it's a wireless LAN itself.
And secondly, there're many different LAN technologies: Blutooth, NFC... What exactly defines WI-FI among these ones? IEEE 802.11? Router, modem?
And one more question: if WI-FI is a wireless LAN technology/protocol, then why is WI-FI accessing to the Internet (WAN)? As far as I understand, local network doesn't have access to the global network. All information exchange happens within the local network, not beyond its borders. Or now "local" and "global" terms become something vague?