A photo library is a library that is stored with photos, these collections can vary from very old to also brand new. Some images are available to the public, but others may have to be payed for. Some individuals may chose to buy these images instead of hiring a photographer for it, this could save them or their company a bit of money.
Photo libraries can be online or on a computer, mobile phone, tablet etc. A photo library is sort of similar to an actual library, but instead of books it is photos. You use photo libraries all the time without realizing, you have one (most likely) on your mobile phone to store your pictures so you can also look at them again later on, your computer and also online you can use photos from or upload photos to an online photo library.
