The sizes you've listed are the sizes for tires/wheels. A hybrid is quite often a 700c which would be very close to a 27 inch wheel, though slightly smaller. Many bikes that came with 27 inch wheels have been converted to 700c. Mountain Bikes generally have smaller wheels (though some called 29ers are actually the same as 700c) than 700c. Some women's bikes and touring bike build with 650c for different reasons.

In terms of the size of the frame that is usually measured by the seat tube - the centre of the bottom bracket (where the crank goes) to the top of the tube. Of course the size can be tweaked a bit by raising the seat post and/or the stem. And to make it more complicated, the traditional frame size is with a top tube that is parrallel to the ground, and many road bike and hybrids now have sloping top tubes. So my hybrid had an 18 inch frame and my old road bike with a standard top tube is 56 (and my new build is 58 or 22.5 inches).