the schematic diagram

A schematic is the map of a circuit, a drawing that shows what connects to what, using simple standard symbols instead of pictures of the real parts. Like a subway map, it does not care where things physically sit or how long the wires are; it only shows the connections. A battery is two lines, a resistor a zigzag or rectangle, a wire a straight line, and a dot where wires join. Once you learn the symbols, you can read any circuit at a glance.

The whole point is that the schematic captures the electrical truth, not the physical layout. Lines are wires; where two lines cross with a dot they are connected, where they cross without a dot they are not. Ground gets its own symbol and appears many times to mean all joined to the common reference. Component values sit beside their symbols (10k, 100uF, 1N4148). You build from a schematic by recreating its connections, whether on a breadboard, a PCB, or in a simulator.

The schematic is the universal language of electronics, the thing you draw to plan, share, and debug a design. A photo of a breadboard is almost useless for understanding; a schematic of the same circuit is instantly clear. Learning to read and draw schematics is as fundamental as learning to read music for a musician, and it cleanly separates what the circuit is from how it happens to be wired up.