difference betweem thumb and image
What is the difference between a thumb of an image and the image? If I copy and paste a video or photo from my mac Photos to an external hard drive, I only get "thumb" of it, although I can see the image. Will I be able to edit this as usual? Thanks for any help.
MacBook Air (13-inch, Early 2014), OS X Yosemite (10.10.5)