I have read this,so I know what an f-stop is, but what does the number on printed the lens signify?
Is this is the maximum f-stop, the ideal, or something else?
It refers to the maximum f-stop (which is defined as the ratio of focal length to effective aperture diameter). Smaller number means larger opening and more light:
Some (possibly overgeneralized) examples:
Read more about aperture from Wikipedia.
Apart from the aperture numbers appearing on the aperture ring, prime lenses sometimes have an additional number of f-numbers printed on them, symmetrical about a central line, most often towards the body of the camera:
They indicate depth of field for a given aperture. For the lens in the picture the selected aperture is f/5.6. Follow the lines starting at the 5.6 at the bottom and you arrive at 7m and infinity resp. So here your depth of field goes from about 7m to infinity.
So, yes, all good information in other answers. The f-stop or f-stop range printed on your lens is its maximum.
You mentioned the ideal aperture.
The maximum is good for allowing you to take photos with less light at shorter exposure times, and in many situations, where the subject or you are moving, it can give you the sharpest results. But not always. Landscapes, architecture, and still life are examples of situations where you will want something else.
So, the max is great but not always the best.
Another consideration is that beyond f/16 or so (in 35mm and smaller formats) you get increasing diffraction. With larger formats, the ideal becomes smaller. Large format lens ideal aperture are more like f/22 and diffraction is more of a problem at f/45.
FWIW, another rule of thumb i've heard (less often) is: ideal aperture is 2-3 stops below wide open.
The number printed on the lens will be the maximum aperture (smallest numerically) of which that lens is capable. There really is no single "ideal" -- for example, as you stop down, the depth of field increases. Depending on what you want and what kind of picture you're taking, under what circumstances, etc., you might want to minimize, maximize, or carefully choose the depth of field (e.g., I want my subject as sharp as possible, and this book in the background blurred enough that the text is no longer readable, but still sharp enough that it's recognizable as text and a book).
When printed on a lens the f-stop is usually expressed as a ratio with a colon (i.e. 1:1.4) rather than the more usual f/1.4, however it still refers to the maximum apparent aperture divided by the focal length.