What does a colon in URL mean?

Question

I've seen this image URL today and I'm wondering what is this ":small" at the end. Is this something related to the CMS used by Twitter? Or can this be used with any image URL?

https://pbs.twimg.com/media/B9GOfXNIIAAxb0H.jpg:small

Thanks

Answer 1

colon ":" is not a special character in the url encoded strings, so the :small is part of the requested file name. The server side code use these flags in this case to be able serve the images in different size.