Prior to 1066....you didn't have these in England. They come only because of the Norman invasion, and become a regular feature of the British landscape after the invasion.
A basic description? It's a fort, with a wooden fence, that has a high point for everyone to retreat to.....in really dire situations. A ditch is dug around the high point to make it slightly more difficult for any invading force to make a run against the defenders.
It should be noted.....structures like this are made of earth and wood.....so they don't last.
I settled upon this research because my family tree has this twist that goes past the 1300s....back to the early 1100s and a Motte and Bailey Castle in Pulford....a small village of sorts today in northwest England (just at the Wales border). The family tree kinda ends in this village and the title of the family (for whatever it was worth in those days) revolves around this one-star castle (none of which exists today except an empty field and a marker).
Pictures of Pulford show some slight rolling hills and a stream. Not a single stone remains today of what was at one point the family 'castle'.
Having grown up in the south and noted the "Jim Walter" homes (houses that costs about half of a normal house and usually took four weeks to erect).....I kinda view the Motte and Bailey castle theme as being similar to Jim Walter houses. You get a brief plan from some guy, get some lumber, and get some of your cousins and associates hyped up on free beer, and throw the house or castle together. Luckily, they didn't have castle inspectors in those days.