Oak and ash wood have a very similar grain and is often confused. All oak wood has a radial grain as well as a regular grain. The radial grain is perpendicular to the regular grain. If you look carefully at the end grain of a board you can see both grain patterns. Ash wood has no radial grain; so when you look at the end of an ash board there is only one grain pattern.
When oak wood is sawed so that the radial grain is flat on the surface of the board you will see a grain pattern that some people call "tiger oak"--which is a kind of ripple effect. Makers of antique oak tables often used selected pieces of wood sawed in this manner for the table tops. When oak is sawed in this manner it is called "quarter-sawed". You will never see a "tiger" grain pattern in ash wood.
Ash and oak woods when stained the same color look very much alike because both have an "open" grain pattern that absorbs the stain in a similar way. Ash is often just a little bit more swirly in look that is oak and is very pretty when stained.