Different origami models sometimes start with the same few folds even though the end results might be totally different from one another. Instead of describing the folds over and over again, an author may choose to simply say "start with Origami Base 1". The instructions for Origami Base 1 would have already been given in an earlier page of the book.
Some authors may have a battery of bases which are specific for the origami models in their book. However, there are only a handful of common origami bases universally recognized by the origami community.
This page shows you how to make an origami kite-base. It is one of the easiest origami bases. It is used in making the traditional origami swan.