There is none.
Quite simply, in an exam sense there is no difference between outline and describe and so if you’re worried about “meeting the demands of the command term” and trying to understand the nuances between these, don’t bother.
There is one difference – the definition. A “detailed” (describe) account versus a “brief” (outline) account. But if you think about it, who decide’s what’s brief and what’s detailed?
In Paper 1 Part A you’re asked to demonstrate knowledge and understanding of research. If you’re asked to describe something, why not be as detailed as possible? Why would you run the risk of being “brief” in case the examiner mistook your understanding of the command term outline for a lack of knowledge?
If you see the word “outline” just think “describe”. Do not worry about the differences between these two learning outcomes, especially in the SAQs.
What’s more important than fretting over the subtle differences between the command terms is understanding the rest of the question. This is where I see too many students make mistakes.
For example, I read a lot of answers to the question “Describe schema theory” that have a two sentence description of schema theory and 300 words of showing how schema theory is demonstrated by Bartlett’s War of the Ghosts study. This is not what the question is asking!
What’s more important than understanding the differences between individual command terms is having a conceptual understanding of what the three different levels of command terms look like.