Spam filters are tools used by email services to identify and block unwanted or harmful messages, commonly known as spam. They analyze incoming emails based on various criteria, such as keywords, sender reputation, and user behavior. This helps keep your inbox clean and safe from potential threats. When a message is received, the spam filter assigns it a score based on these criteria. If the score exceeds a certain threshold, the email is marked as spam and moved to a separate folder. Users can review this folder to ensure that legitimate emails haven't been mistakenly filtered out.