Hi Fifth Musketeer,
Vegemite is a yeast extract. It's similar to Marmite (a British yeast extract that's not nearly as yummy as Vegemite )
It's a dark brown spread - quite salty. Definitely an aquired taste.
We Aussies are brought up on our Vege. Most of us love it.
It's high in B Vitamins, in fact it used to be prescribed for little babies. The mum would put a pea sized scoop into a bottle of boiled water and bub would screw up its nose then eventually drink it. No wonder we're addicted - we were fed it from the cradle.
I don't think it compares to anything American. Mind you the company is now American owned!
Cheers, Fifth!

Rosebud