What is 'Partial Shade'?

[PetBazaar]

Here's a definition from gardening.about.com

Partial Sun / Partial Shade: These 2 terms are often used interchangeably to mean 3 - 6 hours of sun each day, preferably in the morning and early afternoon.

- However if a plant is listed as Partial Sun, greater emphasis is put on its receiving the minimal sun requirements.
- If a plant is listed as Partial Shade, the plant will need some relief from the intense late afternoon sun, either from shade provided by a nearby tree or planting it on the east side of a building.

[astral276]

I think I'll put the plants where I wanted them. That area receives direct sunlight for part of the day and shade the rest as the sun traverses the sky. They have two choices - live or die. Most things I want to grow die anyway. It's only the weeds that seem to thrive.

[Affordapool]

As an ex commercial nursery grower, specialising in bedding and exotics i can sympathise with your question. even int he commercial side of gardening the phrase is a funny one and interpreted in different ways. Especially as different plants, even different varieties of plants will take varying amounts of sun despite liking shade!
I have seen full shade loving hostas doing well in a hot 'sun all day' flower bed and sun loving salvias thriving in a sunless spot!
The key to this seems to be the strength of the sun when it is in it rather than time.... the 12 till 4pm slot is the hottest sun and will be what partial shade lovers want to avoid. In the bedding plant world this would be begonias, busy lizzies, fuchsias, mimulus etc... although again with plenty of water they seem to do ok even when subjected to full sun!
It's a confusing world and yes often trial and error is the only real way!