If it's an amp effect, then it probably doesn't have many variable settings (e.g. feedback, effect level), so I'm thinking maybe it has to do with the type of delay. For example, "echo" sounds to me to be referring to a longer, lower wet signal, type of delay, whereas "delay" sounds like a shorter, slapback type delay. This is all in terms of effects that I would expect to see on an amp.

But, Death55 is right in saying that echo and delay are the same effect, AFAIK.

The best way to figure out the diff. would be to simply play with the amp.