Partial Seams is a technique used to attach a piece of fabric that is longer than an adjacent piece.  For example, the block shown on this page has a central square that is shorter in length than the pieces that surround it.

First, sew pieces A & B together, but stop about 1/2″ from the end. (In other words, you only sew the seam partially.) This first partial seam has made the unit large enough to sew on the remaining pieces.  Next, sew piece E to the straight edge of the AB unit. Then sew piece D to the straight AE side of the unit.  Next, sew piece C to the straight AD side. And finally, complete the seam to pieces A & B, which will now extend into piece C.