Stereo microscopes produce a real stereo image (a visual feeling of 3D), whilst simple binocular or trinocular microscopes merely come with two eyepieces for a higher comfort of viewing in compare to looking through just one eyepiece. Basically, all stereo microscopes are binocular or trinocular microscopes as well, but not all binocular or trinocular microscopes are stereo microscopes. So, if you see a microscope with two eyepieces, it doesn't necessarily mean that it's a stereo microscope. Stereo microscopes have a useful magnification of up to 100x, therefore if you see a microscope with maginfication 1000x and two eyepieces, that's a simple binocular microscope, but not stereo. Trinocular microscopes differ from binocular microscopes with the ability of taking images from the (usually) top of the microscope. Many stereo microscopes can do the same.