The short answer is Self Distribution is: Self - You doing the work and Distribution - getting you book out there. Everyone seems to understand Online Distribution and Bookstore Distribution but when it comes to Self Distribution most people either really want to do it or really don't want to do it and yet neither group of people seems to really know what it means.
As the name implies it is what you do yourself but you can be smart with what you do yourself and how you manage your time and advertising budget and you can be not so smart. Smart Self Distribution markets your book not to your customer but to where lots of your ideal customers go.
For example: don't try to sell your book to everyone you meet in 1 day but offer to go and speak for free to a group of people already interested in your subject matter eg. a children's book would be ideal at a pre-school around pick up time. You want the parent's to see how much fun their children have with your book before they leave so they buy a copy on the way home.
Also be smart about promoting the event. Don't waste money printing advertising when you can email it out. Better yet pass details onto others to email on for you. For example: get the pre-school to send an email to all parent's to let them know if they come 30mins early to pick their child up they can hear the special author's talk their children are receiving.
For more information on self distribution, check out 'How to Publish a Book for Pleasure, Profit or Publicity' THE SEMINAR or 'How to Publish a Book for Pleasure, Profit or Publicity' THE BOOK