An animation key frame is a single still image in animated layers that show action at an important point in that sequence; key frames are defined throughout an animated sequence, in order to define pivotal points of motion before the frames in between are drawn or otherwise created to “tween” the motion between the two key frames. One example of key frames could be an animation of a swinging baseball bat; the bat at rest would be one key frame, and the bat at the end of of its swing would be another.
Keyframing is the process of assigning a specific parameter value to an object at a specific point in time. You can fill the screen exactly five seconds into your project. When you set more than one keyframe.If you want a title to change from green to blue over time, you would set two keyframes at two different points in time. The first one would define the text’s color as green, and the second keyframe would set the color to blue. Motion automatically makes the frames between those points change smoothly from green to blue.
A sequence of key frames is where movement catches the viewers eye, whereas the position of the key frames on the film, video, or animation defines the time of the movement. Because only two or three key frames over the span of a second do not create the illusion of movement, the remaining frames are filled with in between.
In software packages that support animation, especially 3D graphics, there are many parameters that can be changed for any one object. One example of such an object is a light (In 3D graphics, lights function similarly to real-world lights. They cause illumination, cast shadows, and create specular highlights). Lights have many parameters including light intensity, beam size, light color, and the texture cast by the light. Supposing that an animator wants the beam size of the light to change smoothly from one value to another within a predefined period of time, that could be achieved by using key frames. At the start of the animation, a beam size value is set. Another value is set for the end of the animation. Thus, the software program automatically interpolates the two values, creating a smooth transition.(https://en.wikipedia.org/wiki/Key_frame)