What is Stacked Address in bitcointalk account & Private Key

[crypto_altcoins]

Hi,
Can someone explain me what is stacked address in bitcointalk account and also about the private key associated with account. and their use.

[OmegaStarScream]

The private keys are what allow you to spend funds from your address or a proof the address ownership by signing a emssage, wallets like Electrum give you control over those but exchanges like Coinbase etc. don't. People stack/post their address on the forums so If their accounts get hacked later, they could sign a message using these addresses to prove that they are the actual owners of their accounts.