The Konami code is one of those Easter eggs that has long since travelled outside of its origins. It first appeared in the seminal shooter Gradius in 1986, but came to prominence in the west thanks to the NES release of Contra (it is sometimes called "the Contra code"), and basically gives the players bonuses depending on the game: in Gradius you got all the power-ups, in Contra you got 30 lives.
Funnily enough, the code was intended as a debug tool, but someone forgot to remove it and, with Gradius in the latter stages of production, the decision was made to just leave it be. Konami's developers, recognising it was hard to input accidentally but easy if you knew the secret, adopted it as something of a trademark and began including bonuses in many of its games based on the code (usually on the title screen).
