DataMatrix
DataMatrix is a tiny square code, sometimes smaller than a grain of rice, for objects with no room for anything bigger.
What the word means
It has a solid black L along two of its sides and a broken line along the other two. That is how a reader finds it, and how it works out how many squares across the code is.
It has no fixed size: it grows with the text it carries, which is why it can be so small when there is little to say. It is read at any angle, and it reads as well engraved or etched as printed.
What it does on a real document
On a box of medicine it carries the product code, the batch, the expiry date and a serial number unique to that one box. A pharmacy scans it and knows that this exact box was not sold twice.
On a sheet of labels the engine draws one code per label, each with its own text, in solid squares at the size the label allows. It stays readable because the drawing is exact rather than a picture stretched to fit.
Where it comes from, and why
It was made in the United States at the end of the 1980s, for marking parts too small for anything else: electronic components, surgical instruments, aircraft pieces.
The version in use today is called ECC 200. It spreads the text across the whole square and adds spare information worked out from it, so that a code with a damaged corner is still read in full rather than read wrong. It is an international standard under the number ISO/IEC 16022.