At its core, agile is an iterative project management methodology. Agile works by breaking projects down into short duration milestones of user functionality, prioritizing them, and then continuously delivering iterations, usually, in short two week cycles.
Rapid Application Development (RAD) is a type of incremental software development methodology, which emphasizes rapid prototyping and iterative delivery, rather than planning. In RAD model the components or major functions are developed in parallel as if they were small relatively independent projects, until integration.
RAD projects are iterative and incremental
RAD projects follow the SDLC iterative and incremental model:
During which more than one iteration of the software development cycle may be in progress at the same time
In RAD model the functional application modules are developed in parallel, as prototypes, and are integrated to complete the product for faster product delivery.
RAD teams are small and comprised of developers, domain experts, customer representatives and other information technology resources working progressively on their component and/or prototype.