here is a pic of one taken from this post right here at permies.
https://permies.com/t/56013/Brush-berms#468482
It is on contour similar to a swale.
It isn't a ditch that is made by digging down it is instead a mound that is piled up.
But I think you might be asking "what is it good for".
Is it good for >absolutely nothing".
It's a depression like a swale that lets water soak in, vs sheet off.
It is not like a raised bed/huglekulture, that I can plant annuals in., etc, etc
It can be a mini-windbreak
It can stop and trap the leaves and other things that are sheeting off the property in a rain.
It attract birds and collect deposits of fertility/manure.
It is a habitat for lots of critter.
You could harvest mushroom form it, if desired.
It slowly
compost so, a super slow compost pile.
It makes your garden look artsy and clean, and soothing.
It could create quasi-terraces,if it traps enough erosion, and leave litter.
It can turn into a hedgerow.
It can be a wonderful border.
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