Focal length is the distance *between the lens and the sensor* when the subject is in focus, not the distance to the subject. 

The term for the distance to the subject in focus is the *focus distance*. The zone which is in focus either side (front and back) of the subject is the *depth of field*. This varies with the aperture - depth of field increases as the aperture gets smaller (f-number gets larger). All else being equal, depth of field is greater at f/4 than at f/2.

So if you focus on an object 3 meters away with a focal length of 18mm and aperture of f/11, everything from 1m to infinity will be in focus. However, if you focus on the same subject with the same aperture with a focal length of 135mm, the near focus limit is 2.9m and the far focus limit is 3.1m - the depth of field is only 20cm deep, in other words.