It's "part sun" (or "partial shade"), but you will need to understand your plants more intimately than just knowing whether they like "part sun" or not.

Rhododendrons (all of them, including azaleas) grow naturally at the edges of forest clearings. Knowing that - firmly understanding that and what it implies - is the clue you need to be succesful with them.

Your garden site isn't a replica of such a forest clearing edge. It's more like a ravine with a southern or southwestern exposure, so you're going to need plants that can handle full sunlight when they get sunshine, yet also tolerate having less than a full day of sun.

There are a lot of plants that will do that, but you will probably be better off with plants that will grow well in full sun than you will with plants naturally found in locations that are partly shaded all day.

I have a similar spot and I plan on choosing plants that are labeled as Sun to Part Shade. Like the other poster mentioned you need plants that can do well in full sun because the sun they'll get is strong and hot, however they do not get a long enough amount of sun as is needed for plants that require full sun. So far I've tried planting asiatic lilies, foxglove, purple coneflower, dianthus barbatus, and a butterfly bush. The coneflowers where grown from seed so they should flower this year, from what I know about them they should do good in this situation. The butterfly bush had been in a pot too long and transplanted too many times by the time it found it's home there so It hadn't bloomed the last 2 months of summer, so we'll see if it does better this year. I have noticed they need a lot of sun though, so maybe not. The dianthus again was seed started so I won't see blooms until this year, but the foliage was very happy growing there. The foxgloves did not do well there, they bloomed well but the leaves were all burning up and in the fall I moved them to a spot in afternoon shade. Asiatic lilies did well but the flowers tips started fading the day after opening and did not last long at all, so I'm going to say they aren't a good candidate. In the fall I planted some bareroot daylillies there and I have high hopes for those. If you like daylilies I think reblooming tpes like stella d'oro would be best, so you'd have flowers from them for a while. The ones I tried are called purple d'oro because yellow is my least favorite color for flowers, but those d'oros are impressive! Again there might be the problem of the flowers fading much faster with the hot afternoon sun blazing on them, but some varieties claim to be more sun resistant than others, so you can go with those. I found one claim from 'Frankly Scarlet' which I will have my eyes out for at the garden centers. Also I think Rudbeckia may work there as well. Just remember the short amount of sun will cause plants to come into season much later so stay away from things that normally don't bloom until fall or they probably won't bloom before frost kills them back. I found this out the hard way.