user15375: In Logical Chess: Move By Move by Irving Chernev (1957), in Game 3, it reads

Emanuel Lasker, World Champion for 27 years, says of this move, “In my practice I have usually found it strongest to post the knights at B3, where they have a magnificent sway.” Here ‘B3’ refers to the squares c3 and f3 for White, or c6 and f6 for Black.

What type of notation is this "B3" Emanuel Lasker mentioned?

user32606: This is descriptive notation, a composition where the letter B stands for bishop and the number 3 for the third rank from either players view.
Thus, as mentioned in your box, B3 may refer to the squares c3, f3, c6 and f6.
More conclusive for the specific squares is the inclusion of Q or K for queen(side) and king(side), so the square c3 is QB3 (read: queen's bishop three) from white's or QB6 (queen's bishop six) from black's view. An overview is given by the picture below.
A white's knight move to c3 (Nc3) in descriptive notation is N-QB3 (read: knight to queen's bishops three / third).
Descriptive notation has generally been given up upon, because confusion can arise, as each square has two names. This problem doesn't exist in algebraic notation.


15375: <p>In Logical Chess: Move By Move by Irving Chernev (1957), in Game 3, it reads</p>
<blockquote>
<p>Emanuel Lasker, World Champion for 27 years, says of this move, “In my practice I have usually found it strongest to post the knights at B3, where they have a magnificent sway.” Here ‘B3’ refers to the squares c3 and f3 for White, or c6 and f6 for Black.</p>
</blockquote>
<p>What type of notation is this &quot;B3&quot; Emanuel Lasker mentioned?</p>
 32606: <p>This is <a href="https://en.m.wikipedia.org/wiki/Descriptive_notation" rel="noreferrer"><strong>descriptive notation</strong></a>, a composition where the letter B stands for <em>bishop</em> and the number 3 for the <em>third</em> rank from either players view.
Thus, as mentioned in your box, B3 may refer to the squares c3, f3, c6 and f6.</p>
<p>More conclusive for the specific squares is the inclusion of Q or K for queen(side) and king(side), so the square c3 is QB3 (read: queen's bishop three) from white's or QB6 (queen's bishop six) from black's view. An overview is given by the picture below.</p>
<p>A white's knight move <em>to</em> c3 (Nc3) in descriptive notation is N-QB3 (read: knight to queen's bishops three / third).</p>
<p>Descriptive notation has generally been given up upon, because confusion can arise, as each square has two names. This problem doesn't exist in algebraic notation.</p>
<p><a href="https://i.stack.imgur.com/OHbPT.png" rel="noreferrer"><img src="https://i.stack.imgur.com/OHbPT.png" alt="enter image description here" /></a></p>
