However, to be clear, there are a number of different types of instrument with distinct features and names, that we might call, in general terms, gongs.

Strictly speaking a "Gong" has a defined fundamental pitch and its higher overtones are often quite subdued. On the other hand, a "Tam Tam" does not have a defined fundamental pitch and instead has a very crashy or washy, overtone-rich sound. I have heard it said that the difference between a Gong or a Tam Tam is whether or not the instrument has a rolled-over collar or not. This factor often correlates, but there are also many exceptions (a Chau gong for example), so it is not a correct assertion.

There are, of course, hybrids which have a combination of defined fundamental pitch and an overtone-rich wash. I have made many hybrid gongs like this. They tend to morph from Gong to Tam-Tam depending upon how hard they are struck and, also, where they are struck, what size mallet is used, etc.

Beyond strict Gongs, strict Tam Tams and hybrids of the two, there are things like "Plate Chimes", or "Bell Plates". These are usually relatively small and quite thick and heavy for their size. They may be suspended at the edge or at nodal points. They have a very clear, chiming, bell like sound with a long sustain and a relatively ordered and minimal overtone spectrum (certainly when compared with a Tam Tam). My "Naan" chimes are an example of this.

One of the things I specialise in are "Sculptural Gongs". These are non-round gongs of often quite ornate design. Generally, these fall into the Tam Tam sound bracket.

Singing bowls are sometimes referred to as gongs. Strictly speaking, they are a type of bell. In ancient Tibetan culture, the pure sound of the bowls was said to frighten away demons or evil spirits.

"Opera Gongs" with their characteristic ascending and descending tones fall into the strict Gong classification. Even though their fundamental pitch is variable, it is still clearly defined.