Generation Gap
When someone has a big gap between their front two teeth. E.g. Michael Strahan
Did you see that girl's generation gap? Man it was huge.
Generational Gap
When your sister posts naked pics of herself on the internet, then claims you don't understand the industry she is in.
-Hey Fred, out in L.A., we use those pics for our industry, you just don't understand! There must be a Generational Gap.
-But Rebecca, you work in Social Media!
-But Rebecca, you work in Social Media!
Generation gap
In today's usage, it refers to a perceived gap between younger people and their parents or grandparents.
Generation gap should have been solved in the future