what is the oil in "vinegar and oil" ??

The oil is any kind of oil you like; canola, olive, vegetable, etc.

If you are trying to make a vinegar & oil dressing, most people use olive oil and for the vinegar part, I like to use basalmic. If you add a bit of salt, pepper and pressed garlic, you can have a great salad dressing in a matter of minutes.

Hope this helps.

For salad dressing, vinegar and oil is normally balsamic vinegar and olive oil.

A lot of times it is olive oil; but it does not have to be. It can be corn oil, vegetable oil, nut oil, avocado oil, or any number of oils from vegetables or nuts and fruits.

Something generic, like canola or vegetable oil. If you are to use a stronger one like balsamic, the recipe would say so.