For historical information about Aurum, see the EVE Uni Wiki page.
Regarding ETC’s they were 16 character codes that could be redeemed in game for a 30-day Pilot’s License EXtension (PLEX)*, an in-game object that could be sold for ISK or activated. ETCs were available through third-party partners (and I think direct from CCP, though not really sure). ETCs replaced the old GTCs (Game Time Cards) which were physical cards with a code under scratch-off foil.
* At the time, PLEX was only used for game time, not for any other in-game purchases. When microtransactions were introduced with WiS/CQ, the conversion rate was one PLEX to 3500 Aurum. Aurum was the currency for buying apparel and augmentations until PLEX was re-factored 1:500 and Aurum was removed from the game.