This is because as fast as light is -- moving at the speed of light -- it isn't instantaneous: at 299,792.458 kilometers per second (186,282 miles per second), it requires that length of time to ...

If you want the instantaneous speed according to the definition 2, that would also be 20 m/s. It's all about definitions. Suppose we want to have a discussion about gardening.

Again, this is usually used as "instantaneous speed". Basically, this is how fast something is going. Velocity is a vector, and speed usually means the magnitude of this vector.