What is the meaning of widely patent gastrojejunal anastomosis?

It means that there is a connection between your stomach and a part of your small intestine called your jejenum, that is open.

If you imagine your stomach leads into your small intestine, which is subdivided into three parts.

Your duodenum, jejenum and ileum.

So the gastrojejunal anastomosis bypasses the duodenum, which is involved in food digestion.