The key properties available here belong to special, animated elements (e.g., several color gradient settings such as knot interpolation).
The key is located at this time in the animation.
Activate this option if you want to protect a key from inadvertently being edited.
See Breakdown Color.
Use this setting to mute a key. When a key is muted, any interpolation or change in value(s) between the muted key and the subsequent key will not take place. Once the animation reaches the next key, values will instantly jump to those contained in that key. Muting a key turns the animation for that key off until the next key is reached.
Here you will occasionally find different settings listed (e.g., for an animated color gradient) that correspond to the respective animated elements.