The velocity working as a rotational or circular motion and touching only at one point is called as tangential velocity.
Take for example a bi-cycle:
When you are driving a bi-cycle the wheels are performing rotational motion. But the wheels are only touching the ground at one point only.
This above example shows that there is tangential velocity.
In circular motion, take this example:
You have tied a stone with a string (The good old string- stone example). You start to give it a motion in a circular orbit. At any instant or in very short time, on the imaginary orbit the stone is touching only a single point.
This is known as the tangential velocity in a circular motion.
That also how our planets revolves around the sun, the satellites revolves around the planets, etc.
The image shows that the planet has tangential velocity around the sun.