A "vague idea" means having a general understanding or a blurry concept about something without knowing the specifics or details.
Sentences with «vague idea»
That's not all: the theater in which they operate will have to close within a month and the men and women have only vague ideas of what lies ahead. (shockya.com)
You are simply thrown into a terrifying world with a very vague idea of what to do, but after that you are on your own. (condemnorcondone.com)
By using specifics, you'll avoid vague ideas as well as generalized statements. (essaycaptains.com)