Modbus is a protocol that lets a "client" request data from or write data to a "server" - typically between a controller or PC and sensors or actuators in an industrial environment. It operates over serial links (such as RS-485) and over Ethernet via Modbus TCP.

One of Modbus’s strengths is its simplicity and wide support. Because the specification is open and royalty-free, many vendors have implemented it, resulting in a large ecosystem of compatible devices and software. That simplicity also means it lacks some modern features like automatic bus discovery or built-in security - those need to be handled separately.

In practice, Modbus is still widely used in automation and SCADA systems to collect measurements like temperature or pressure from field equipment and forward them to a supervisory controller. Keep in mind you need the device address, the register to read or write, and the supported mode (RTU, ASCII or TCP). It’s not plug-and-play with automatic tags the way some modern systems are.