Microformats are small patterns of HTML used to publish commonly occurring information like people, events, reviews and tags in a structured way on web pages. They allow information to be machine readable without changing existing behaviors. Microformats follow principles like solving specific problems simply, reusing existing standards, and prioritizing humans over machines. Popular microformats include hCard for contact information and hCalendar for events. Overall, microformats aim to make web data more accessible and searchable.