It *may* be like a yarn over, from what country is the pattern? It may mean YO then knit 1, or just YO. But could be something else. Check every part of the pattern book because it is seriously negligent for them to leave it out. It should be somewhere near the back or front cover , but often will be smack in the middle or randomly placed.
Look at every single page for a few seconds, don't just flip through.
If they have left it out, your most reliable answer is from Paton's themselves. Make sure it's the right branch/country website that gives you the number! If you e-mail them, it may be helpful to give the year of printing, or even scan in the whole pattern.
Does the stitch count help you at all?