Hello there antonietta,
Welcome to the Q&A Board. I believe you are speaking about what is known as
35 mm equivalency. Digital camera manufacturers describe focal lengths in terms of the lens length on a 35 mm camera which would produce a similar area of view. While the focal length on one 35 mm camera is the same for all others, it is not the case for digital cameras.
Here is more detailed information and a chart about 35 mm equivalency:
http://www.digicamhelp.com/what-is-35mm-equivalent/
