What is Focal Length? Is it anyway related to depth of field?

Answer 1

Focal length is the distance it takes a lens to focus an image onto a surface, especially within a camera. Depth of field is how much of your image is within the precise area of focus, here we are talking about a, "front" to "back" effect, which is why it is "depth" of field. Focal length is fixed, depth of field is variable.
Depth of field is controlled by use of "f" stops. As an example, a lens set to f1.8 has a shallower depth of field than a lens set to f13.

Answer 2

I suppose this is about cameras.
If we have a single lens, the focal length is the distance from the lens to the film when an object at infinite distance is sharp on the film. (normally a distance of a few hundred times the focal length is considered infinite)
A longer focal length have a shorter depth of field.
This can be a problem (or a benefit) of digital cameras which generally have shorter focal length for the same image, Its not so easy to get the background out of focus.