What is a spike called when it is seen as a front moving along the axon, and how long is that front? · Lobeworks/17

A depolarisation wave (a wave of depolarisation).

What is a spike called when it is seen as a front moving along the axon, and how long is that front?

A depolarisation wave (a wave of depolarisation). It is the stretch of axon whose membrane is flipping positive at a given moment, with resting membrane ahead and refractory membrane behind, and it moves because each stretch drives the next one to threshold. Its length is the conduction speed times the spike's duration of about a millisecond: around a millimetre in a bare fibre at 1 m/s, around ten centimetres in a myelinated one at 100 m/s.