Transactional email refers to automated, one-to-one communication sent by businesses to their customers in response to specific actions or events, such as order confirmations, password resets, receipts, and shipping notifications. Unlike marketing emails, which are promotional in nature, transactional emails provide essential and timely information related to individual user interactions with a website or application. They are typically triggered by user actions and are critical for maintaining customer trust, enhancing user experience, and ensuring the smooth functioning of online transactions and services.