Tweening, short for "in-betweening," is a technique used in animation to create smooth transitions between two key frames. Key frames are the main points of action or change, while tweening fills in the frames in between, making the movement appear fluid. This process can be done manually or with the help of software, which automates the creation of intermediate frames. In digital animation, tweening is commonly used in programs like Adobe Animate or Toon Boom Harmony. It allows animators to save time and effort by generating the in-between frames automatically, ensuring a consistent and polished final product.