What does the symbol shaped like --{ }-- represent in a ladder diagram?

The symbol shaped like --{ }-- in a ladder diagram indeed represents an imaginary coil that will activate a digital output contact when energized. This symbol functions conceptually to demonstrate how certain control logic operates within the system.

In a typical ladder diagram, the imaginary coil acts as a representation of an internal state or condition that can change when the circuit logic conditions are satisfied—this mimics the behavior of physical devices without representing any physical component. When the coil is "energized," it signifies that the associated output, such as a relay or contact, will be activated according to the logic defined in the ladder diagram.

This understanding of the symbol is fundamental in programming and interpreting ladder logic diagrams, as it reflects the flow of control and the relationship between various inputs and outputs in a Programmable Logic Controller (PLC) system.