Slowcoach felt sure he had finally crawled into a position from where he could haul himself through Topology from the Differential Viewpoint by John Milnor. Imagine his humility when, on the very first page of the book, his march to victory was gunned down by a simple piece of notation.
$ \mathbf {Definition} $ A subset $ M \subset R^k $ is called a smooth manifold of dimension $m$ if each $x \in M$ has a neighborhood $W$ A $M$ that is diffeomorphic to an open subset $U$ of the euclidean space $R''$.
Here is a screen shot of the fly in the ointment – I didn't know how to render it using MathJax so used instead the easy option of capital letter that looked like it.
And a screenshot of the brief prelude to the definition.
So there we have it: what does the A in WAM mean?
I am posting this as an answer because I cannot post images in comments. However, I believe that this question is off-topic for Math SE, as question is ultimately the result of a rendering error, and is not mathematical in nature.
This is a problem with the rendering of the font in the version of the text you are reading. The top Google hit (in my Google bubble) is a .pdf document which contains this error:
However, in the preview of the same text on Amazon, the passage is rendered as
I suspect that the document you are reading is an OCR'd version of the original text which has not been proofread or copy edited to catch these kinds of mistakes. Note, also (for example) that the $\varepsilon$ is not rendered correctly in the same line, and that $R^m$ is rendered at $R''$. I would suggest that you find a different copy of this text.