Don't be surprised if you receive as many different answers, as there are number of respondents!
This is the way I consider it, Part sun will generally indicate morning sun for a period of 3-6 hours or late afternoon sun for a similar period or dappled shade, where there is more shade than sun during the day, provided by tree canopies.
Part shade, to me, means that the emphasis is on more direct sunlight, with a period of shade during the hottest part of the day, just after noon to mid-to-late afternoon. Dappled sunlight means more exposure to sunlight during the day and less shade provided by the canopy.
I have seen some descriptions that completely reverse the ones quoted above,i.e., Partial shade meaning a few hours of morning sun and shade the remainder of the day, so be aware!
Rb

I have always been confused about this as well. rb33 -- So, in short, are you saying Part Sun = More Shade than Sun and Part Shade = More Sun than Shade?

Ughh, this is probably why initially I move things around so much! You find out something just doesn't bloom well or it's getting fried.

Anyway, I don't have the code figured out!

Well I have always thought they meant the exact same thing. Like is the glass half empty or half full? Walter Reeves seems to use the terms interchangeably in this link.

Here is a link that might be useful: Walter Reeves

The front of my house faces west, so the July and August afternoon sun can really fry plants. My experience is the both part shade and part sun plants can handle the morning sun, but few of them can handle the afternoon sun. Afternoon sun generally means that I will need to use a full sun plant. Of course, all of this is general. That is why we move plants!

Well, that would be easy to remember: afternoon sun = full sun. You're right woody -- this IS why we move plants. I guess we are all hoping that somebody has the definitive answer so that we can always get it right the first time! LOL (But what fun would that be, right?)

Another complication is time of year. For example on the North facing side of my house - the front - I get 3 or 4 hours of full sun in the mid-day hours in mid May through mid August....however in the winter and fall - zero sun as its cut off by the roof line of the house.

As the growing time for plants is when the sun is available what I dont know is the relevance of no direct sun when the plants are in the fall or dormant winter stages.