A wiki is a type of website that allows users to easily add and edit content using only a web browser. Wikis enable collaboration by allowing multiple people to work together on shared documents and projects. They have various benefits for teaching and learning, such as facilitating group work and sharing of resources, but may also face challenges such as technical difficulties and students feeling uncomfortable sharing work publicly. Wikis can be used in education for activities like curriculum development, group assignments, and providing discussion forums for classes.