A character in physics is usually used for many different things in many different areas of physics, and indeed science. They are only really useful to convey information if people first agree on its meaning. Usually it is quite clear however if a particular use is quite common in the field you might be working in.
As an example, g might represent the gravitational acceleration on a planet in mechanics or something like the coupling strength of a gauge force in quantum field theory.
War symbol
There is no element with the symbol "G." There is Gallium (Ga) and Germanium (Ge).
It means diminshed, so G followed by a degree symbol means play a G diminshed chord.
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The chemical symbol for gold is Au
no element has the symbol G
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I2(g) is the symbol for iodine in its standard state (including its state symbol.)
The abbreviation for gram is gm. and the symbol is g. Gram is short g.
The symbol for Genpact Limited in the NYSE is: G.