NoIslandsSans is a OpenSans font clone without loose islands/insets - ideal for CNC cutters
On the capital latin characters (and arabic numbers) the islands have been "cut open". That is, bridges connect the former outer and inner parts of the character elements. When cut along its outlines, the characters should not have parts falling out.
The 88 units refer to the width of the bridges. The glyph for "A" is 1468 units high, so the bridges are roughly 6% the height of that character.
To edit the font, use FontForge.