If you read at digital video cameras specifications, you will probably read that camera has 20x optical zoom or even greater.   

If you compare this camera with my Nikor 18-200 lens, the lens itself is much bigger then digital video camera, but digital video camera has bigger optical zoom. How this is made, and why my lenses are so big in compare with digital video cameras?  

Term digital video camera is referencing to devices which is used for recording video in first place.