What is spread, exactly

[madpear]

I don't consider myself a noob, but this is definitely a noob question.

I use D-pad 2 hands, right hand index on up, right hand middle on right, left hand index on down, and left hand middle on left.

Everyone says spread is great, and I believe it, and I even think that I might be using it and not knowing it. But what I want to know is exactly what the definition is, and what people like Shashakiro use exactly.

Thanks