A number of small fails performed in quick succession, creating a chain of fails.
Matthew slipped on the wetdeck at the front of his house, which caused him to fall down the stairs onto the pavement, landing in a pile of dog faeces that his pet left there. Chainfail!
When you can't make links, pics, or videos work in your posts on forums. You try to share a pic, but all the readers see is a red "X" at best. You try to share links, but everyone that tries to follow them get a collection of 404s. You try to share a YouTube video, but embedding has been disabled. Basically, you can't grasp some of the easiest internet related concepts.
Dayum, Jake can't get any of them pics working in the forumtoday... total chefail!