Modules are devices that allow for machine to machine (M2M) communication across a variety of networks, both transceivers (TX & RX) and receivers (RX only). Cellular modules are the most common wide area transceiver and they facilitate communication over cellular networks like 4G or 5G. Other transceiver modules can communicate over shorter distances and lower power, Zigbee WiFi, Bluetooth, Bluetooth LE and LoRa are examples. GNSS and GPS receivers are GPS modules that must have their information, like Position Velocity and Time (PVT) transmitted over a communication network.
Everything from phones, cars, medical equipment, vending machines and large machinery can have cellular modules installed in them.