file reference with slash

If I am referenceing a file (lets say开发者_运维问答 an image file for it to display on a webpage) which is a few folders above, I can write "folder1/folder2/file.jpg". What does it mean if the reference starts with a slash like "/folder1/folder2/file.jpg"?

Leading slash means that the reference is starting from the root directory (absolute reference) vs. the current location (relative reference).