What is a Tangent?

In the app below, [b][color=#9900ff]the line you see [/color][/b]is said to be [b][color=#9900ff]tangent[/color][/b] to the circle. Interact with this app for a few minutes and then answer the question that follows.
Note: LARGE POINTS are moveable. Be sure to drag them around!
Note, in the app above, a [b][color=#9900ff]tangent line[/color][/b] has to intersect a circle. [br][br]Yet what, specifically, does it mean for a line to be [b][color=#9900ff]TANGENT [/color][/b]to a circle? [br][br]If you're still not sure, check out the app below.
Note: LARGE POINTS are moveable. Be sure to drag them around!
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Information: What is a Tangent?