T-shirt sizing is a method used to estimate the relative size of a task or project in agile project management. It typically involves assigning sizes like XS, S, M, L, and XL to represent the complexity or effort required. This approach helps teams quickly gauge the scope of work without getting bogged down in detailed estimates. The process usually occurs during planning sessions, where team members discuss tasks and reach a consensus on the appropriate size. T-shirt sizing promotes collaboration and encourages open communication, making it easier for teams to prioritize work and allocate resources effectively.