Reference Clauses of the Act : Art. 2, item (i) and Art. 48, para. (4), item (i)
It means gas in a state of its volume being decreased (compressed) under pressure. Some substances turn into liquid when compressed, and compressed gas is a substance in a gaseous state which is compressed to an extent that it does not turn into liquid.
In addition, a gas of the gas phase when it is filled with a liquefied gas in a container shall be handled as a liquefied gas.
ref. High pressure gas and liquefied gas