There are different kinds of keyframes you can set, depending on how you intend to use them. They include the following:
Key
A normal keyframe, often called a key, has the interpolation, time, and value that you set for it. It has no additional characteristics.
See Key button for more information.
Zero key
A Zero key is a keyframe with a value of zero. A Zero key can have any type of interpolation.
FCurves pane A. A Zero keyframe with Auto interpolation and flat tangents
You can use Zero keyframes to define the start and end of an animation. You can also set the effect of a layer to zero at a given time using zero keyframes.
Zero keyframes work on individual or multiple properties. With multiple animation layers, a Zero keyframe means there is no offset on this frame relative to the previous layer.
For example, if you have two layers and you do not want the animation from Layer 2 to affect Layer 1, set a Zero keyframe on Layer 2 so that it is not offset from Layer 1.
See Zero button for more information.
Flat key
A Flat key is a keyframe with flat tangents and Fixed interpolation. In the FCurves window, you can see that a keyframe’s tangents are flat when its tangent handles are horizontal.
If your character’s feet go through the floor, setting a Flat keyframe at that point prevents the slope of the original animation from overshooting or undershooting.
Flat keyframe A. Keyframes with flat tangent handles
See Flat button for more information.
Discontinuity key
A Discontinuity key is a keyframe with discontinuous tangents and Auto interpolation. A discontinuous tangent points directly towards or away from the next or previous keyframe.
Discontinuity keyframe A. Discontinuity button B. Keyframes with discontinuous tangent handles
See Discontinuity button for more information.