Hot Wallet
A wallet whose private keys sit on a device connected to the internet, so transactions can be signed quickly.
Hot wallets cover browser extension wallets, mobile wallets, and the operational wallets an exchange uses to process customer withdrawals without human intervention. The convenience is immediate signing; the exposure is that malware, a phishing site, or a compromised server can reach the key or trick the owner into signing a harmful transaction. Operators normally keep only a small working portion of total assets in hot wallets and move the remainder into cold storage on a schedule. The category is defined by connectivity, not by the amount held or by the brand of software involved.
In practice
Exchanges publish addresses for their hot wallets so that customers and analysts can observe the operational balance used for routine withdrawals.
The common misunderstanding
A hot wallet is defined by its keys being on a connected device, not by how much value it contains or by which application displays the balance.