What is WIF?
WIF (Wallet Import Format) is a base58-encoded plaintext private key.
The WIF and private key can be used interchangeably, so it can be understood as another form of plaintext private key. If anyone gets hold of your WIF, enters it into a wallet, and sets a password (they do not have to have your original password), they can enter your wallet and have full control over it, compromising your digital assets.
Therefore, you must keep your WIF safe.