What is the definition of close focus for binoculars?

Close focus is the distance between the binocular and the nearest object that can be focused on. In general, binoculars with lower magnification and smaller aperture have a closer focus.

Close focus is important when you want to see something close to you in detail and up close.  This is especially important to birdwatchers and people that look at butterflies, insects, etc.  The ability to determine one species from another can be a very small marking that cannot be seen with the naked eye.