A schematic diagram refers to a particular kind of circuit design that utilizes standard electrical/electronic symbols rather than pictures to demonstrate how a circuit (or part of it) works. Below is a normal 3-wire motor control circuit using a typical momentary halt - start pushbutton channel using a schematic diagram. (Momentary this means the button/switch you trigger will return to its default location once you let go of it, usually by a spring that compels the button/switch to get this done.)
Pictorial design diagrams, or pictorial circuit diagrams are basically the identical thing with exactly the same purpose, but they use images of elements inside the circuit instead of symbols. Again, here's the exact identical precise circuit (virtually except a control transformer was inserted and they are using conductors L1 and L3 instead of L1 and L2.
Right, much less clutter? I have enough information in each of these diagrams to know exactly what this circuit does and also where to search for issues. Hope that this helps. ( Note: do not confuse lecture or circuit diagrams with wiring diagrams; wiring diagrams will usually show images of elements such as the pictorial, and also how the entire or part of a circuit will be wired. The distinction is that wiring diagrams typically put an emphasis on real physical location of necessary components relative to each other that essentially tell a layman Just What to do about the wiring. )
Here's a specialized version of a diagram known as a ladder structure. The primary purpose of this diagram is to demonstrate the logic (speaking to electrical control) of a circuit. This diagram is the one that I mostly come across in my own line of work, and it is very effective for troubleshooting issues or learning the way the circuit works. Some frequencies are so huge that many types of schematic diagrams need to be read in increments from book form (normally with coded numbers so that info can be easier located ). Again, here's the same precise circuit because the first 2, but considering it in ladder type.
Here is another schematic diagram demonstrating the same circuit, connections and components and it looks different but they fall into the exact identical category.
Consider it this way; a circuit structure is any sort of diagram that demonstrates the way the circuit operates where the main objective is the proper wiring of elements and their connection to each other instead of physical location relative to each other or intending prototypes. Nevertheless, in some uses classifying diagrams can be difficult so choose this as general information. I've found this is especially true when dealing with more complex circuits and electronic equipment. I'm going to use a more straightforward but typical industrial circuit since these circuit setups are the exact same, but where it is possible to see how each type of diagram shows the function of the circuit in their own ways.