Wallet keys - a pair of private and public keys from the user’s blockchain wallet. Using the private key of the wallet, the user signs her transactions in the blockchain network (and, accordingly, manages her funds). Traditionally, these are Ed25519 keys and can only be used to sign the data, not to encrypt it.
Communication keys - a pair of the user’s private and public keys (x25519 standard), with which the user encrypts and decrypts messages. The communication public key is known to everyone since it’s published on the blockchain by the user). The communication private key is known only by the user.
Ylide password - a secret password created by the user in Ylide. It is used to access his communication private key on any device by only signing with his wallet (MetaMask/Phantom/Coinbase Wallet/etc.).
Session - from the moment when the user opened the application until the moment when he closed it. An application can be called either a regular application for a computer/smartphone or a dApp running in a browser tab. In the former case, closing the tab is the end of the session.