What is meant by asymmetrical left finding on mammogram when last ten were normal?

I have to believe you mean an asymmetrical nodule, m or density. Asymmetrical is not a thing it is a visual description. The report will explain what was seen. Anything could have caused it or nothing at all. They are not very unusual and not cause for concern. It’s great they have all you mammograms in one place for comparison. Make sure you keep copies should you get a mammogram somewhere else in the future.