– a way of referring to what is properly known as the "public address".
It is similar to a mailing address or email address in that you can share it with others as a means to locate or reach out to you. It is completely safe to share your public address however due to the public nature of data on blockchains, something that the Bitmex hackers forgot, any other user can see your balances with your address.
The transparent nature of blockchain means that if someone knows your public address, it means that they can also view your account balances of that wallet. It is designed this way, and some hackers seem to forget even if 4.5 billion usd worth is on the line.
Hey you can send me some ETH to my address (0x...) for that thing you owe me for...