1 Sallah: Come on. We should get out of here. {leads the way}
1 Prof. Jones: Before breakfast?
2 Sallah: The Nazis weren't going to kill you. They were planning to interrogate you for information on the Aegis of Athena.
3 Monty: The legendary goatskin breastplate of the Ancient Greek goddess Athena? But that's just a myth.
4 Sallah: Like the Ark of the Covenant, the Holy Grail, the Spear of Longinus, Atlantis, and the Palladium of Troy?

It's not entirely clear what the Aegis of Athena actually is. All the sources I've looked at have several different interpretations, with a goatskin breastplate being just one of them. Another popular one is that the Aegis is a shield, although an aegis in general is typically defined as being a cape or collar, made of some form of cloth. It seems to be more of a symbolic item, representing the protection of the gods, rather than something offering physical protection.

Athena, being the goddess of war (among other things, such as wisdom and justice), was the best-known mythological figure to have an aegis, and hers is probably the one most people think about when they encounter the word "Aegis". Just what her Aegis was... well, the myths and interpretations vary widely.

Naturally, we'll learn more about the truth behind the Aegis as this storyline progresses.