What does a table under "Emission Point" label mean in metal-can laser LED mean?
This is Geometric Dimensioning and Tolerancing (aka GD&amp;T). It is a newer and more specific way of dimensioning drawings compared to the traditional way of using dimensions everywhere. It came out of the UK weapons industry during and shortly after WW2, and is quite popular in industries where precise and clearly defined tolerances are important.
I'm not exactly fluent, but if I'm reading them correctly:

A in green is a datum feature Since the green A is attached to a cylindrical surface, it defines and axis down the centre of the cylinder from which other things can be measured.
A at the end of the red box means the measurement is taken from that datum.
The circle with a cross means position, so this control frame is specifying the location of the emission point.
0.17 is a tolerance.  Units will be the same as the rest of the datasheet. In my experience GD&amp;T is almost always metric (but I'm sure there are exceptions in documents from the USA and/or the last century).

So the emission point is within 0.17mm of the axis defined by the cylindrical surface marked A.