This may be biased by my academic background where a sabbatical year is typically one where you would have no teaching duties so were free to travel to another university to work with a new group, explore a new field, finish a manuscript, etc. Expectation is that you are working, but not your routine work.

I've heard it used similarly outside academic contexts and when it was not something you were contractually guaranteed - e.g. "I took a year off my job to finish my book" , but never in the sense of "I took a year off my job to go surfing".

So i guess I think of it as a formalized break from your work routine where you do something else productive with the expectation of going back to that work afterwards.

Of course "productive" here is a bit slippery.