What are keyframes in the context of digital animation?

Keyframes in digital animation are crucial markers that define essential positions of objects at significant points in time, specifically at the start and end of a particular action or animation sequence. By establishing these main frames, animators can create a series of intermediate frames that smoothly transition between the keyframes, resulting in fluid motion and more dynamic animations. This method is foundational in animation as it allows for control over the timing and movement of elements, ensuring that the intended visual effect is achieved.

In contrast to the other choices, frames that serve no purpose do not contribute to the animation's progression and can lead to confusion. Additional frames created for detail, while useful for enhancing the visual quality, are not fundamental to defining the core motion and timing. Lastly, frames that adjust the speed of movement involve more complex timing considerations which may not fundamentally represent the key positions or transitions as effectively as the keyframes do. Keyframes play a central role in the structure of an animation, making them indispensable in the creation process.