abbreviation: Unsymmetric Di-Methyl Hydrazine.Popular rocket fuel in the hydrazine family, combined hypergolically with IRFNA, LOX, or (most often) Nitrogen Tetroxide in modern liquid-fuel rockets. With most oxidizers, a vacuum specific impulse of 350 seconds is easily possible. It's also popular as a monopropellant in satellite applications; because it combusts upon contact with platinum-group metal catalysts, there is no need to carry a separate oxidizer, and all the baggage (plumbing, pumps, mixers, tankage) that goes with a bipropellant system is weight saved.
Despite its superiority as a storable propellant, its toxicity (0.422 mg per liter in 4 hours, inhaled, but also lethal when ingested or absorbed through skin) high density, and cost make it less-than-ideal for most non-military applications.
The chemical formula is (CH3)2NNH2 , in case you want to make some at home, and it looks something like this:
N -- N
If I understand esapersona's Guide to Naming Organic Compounds, this could also be called "trans-dimethyl hydrazine."