First Generation (1G) analogue mobile telecommunications systems (no longer in operation)
2G supports digital standards. Networks support voice calls, text messaging and very-low-speed data connections. All handsets are able to connect to 2G networks.
3G networks support voice calls, text messages and mobile broadband. Most phones support 3G connections, but some older phones and very basic phones do not. When 3G coverage is not available, handsets will try and connect to 2G.
4G networks are currently used primarily to provide mobile broadband. Because these networks are relatively new, users may need to upgrade their handset and subscription to access them. Three supports voice calls on its 4G network on some handsets. The other operators plan to upgrade their 4G networks to support voice services during 2016. Until then, all other voice calls are carried by 3G or 2G. 
5G mobile standards are in development under the auspices of 3GPP. They will offer very high upload / download speeds and very low latency (therefore suitable for many sensory applications). It is expected that 5G will complement and not replace current 4G. In the UK, 5G will be available from after 2020.
WiFi is broadband without wires. It allows electrical devices to connect to a wireless LAN.
A wide-area network (WAN) is a telecoms or computer network that extends over a large geographical area.
A local-area network (LAN) is a network that connects computers within a limited area.
A low-power wide-area network (LPWAN) is a type of WAN with a low bit rate used by connected objects in the internet of things.
The internet of things
General packet radio service – a widely deployed wireless data service.
Global Systems for Mobile communications, the 2G standard developed for Europe (and widely adopted in other parts of the world).
International Mobile Equipment Identity – a unique number on your mobile, usually printed inside the battery compartment.
Your internet protocol (IP) address is the unique number that identifies where you are accessing the internet from.
Multimedia messaging service – the process for sending images, audio and video between mobiles.
The ability for a customer to make and receive calls, send and receive data, or access other services when travelling outside the coverage area of their home network.
Specific absorption rate – the measure of how much electromagnetic radiation is absorbed by the body tissue when using a mobile phone.
Subscriber identity module – used to identify a mobile user.
A smartphone is any mobile with advanced features such as email and internet access.
Short message service – a way of sending text messages between mobiles.