No one checks designators, there's no like universal regulatory process or anything -- at most, in-house standards apply, or only what is dictated by contract terms. There are standards, such as ANSI-Y32.2 (1975), but "TG" is not among them.

The component in question appears to be a multilayer or ceramic component: ferrite bead, thermistor, MOV, etc.. Ferrite bead wouldn't make much sense in parallel with a relatively large resistor, and MOV maybe. A thermistor, for sensing ambient temperature on the board, beside perhaps a comparator to set a threshold, is a definite possibility.

We can't know for sure without tracing the surrounding circuit, knowing what the other components are, connectors, etc.

No one checks designators, there's no like universal regulatory process or anything -- at most, in-house standards apply, or only what is dictated by contract terms. There are standards, such as ANSI-Y32.2 (1975), but "TG" is not among them.

So, it could mean anything.

The component in question appears to be a multilayer or ceramic component: ferrite bead, thermistor, MOV, etc.. Ferrite bead wouldn't make much sense in parallel with a relatively large resistor, and MOV maybe. A thermistor, for sensing ambient temperature on the board, beside perhaps a comparator to set a threshold, is a definite possibility.

We can't know for sure without tracing the surrounding circuit, knowing what the other components are, connectors, etc.