Very simple example - A paper containing one or several relays being in use. The paper describes the component designation, available terminals and their functions and then a reference or page number for each terminal being used in order to be found in the drawing.
The nearest formal name I know of is a "Reference designator"?
Or just index or cross-reference?
But many manufacturers use their own systems.
Some manuals have a component identification section, with outline data on every part used - but few now, it's pretty much gone out of fashion.
Or, some have coordinates, eg. along the top and side of each page, and each sub-component has the page and grid location of the main part.
Some schematics prefix such as relay contacts with either the the page number that the coil and contact arrangement details are on, with the coil having the contact diagram below and all used contacts identified with the wire number, column number or the page / grid location the contact is used, as in the image below.
Some also have mechanical schematics of the control panels/cabinets, with all parts shown in their relative positions, IDs to match the ones in the electrical schematic and with all terminals identified with the wire numbers that connect to them.
There is no single standard, unfortunately.