Fully defined sketches are where all of the parts of the sketch are fully fixed. In other words, no part of the sketch can be moved from its current position. To illustrate this, we will take another look at the sketch we started and fully define it. We will do this by adding an angle of 45 between L1 and L3. The fully defined result is as follows:

Note that the sketch is now fully black on your screen. Also, if you hold and try to move any of the sketch parts, they will not move because they are fully restrained. When the sketch is Fully Defined, SOLIDWORKS will take note of this at the bottom of the interface. Remember that we fully defined a sketch by adding relations and dimensions until all the sketch elements were fixed:

When sketching with SOLIDWORKS, we will mostly try to make our sketches fully defined in order to capture our full design intent. Now, let's look at over defined sketches.