Hydrazine is a composite resource in Astroneer. It is a purple liquid inside of a Canister, with a purple ring on top to indicate the amount of Hydrazine left. It is the only liquid in the game, and it is also the only composite resource that is not a solid.
Hydrazine used to be stored in a Canister, and while it retains its old model it currently does not actually need a canister to be stored. A canister for it is generated when crafted in the Chemistry Lab, and will disappear when used to fuel a Hydrazine Thruster or craft Graphene in the Chemistry Lab.
Hydrazine is based on the real-life inorganic (i.e. not carbon-based) compound N2H4, which has historically been used as rocket fuel or as a component of rocket fuel[1].
When landing with a shuttle using a Hydrazine Thruster, explosive plants on Atrox may destroy your hydrazine (in backpack or attached to the thruster) and thus disabling further travelling.