In plane geometry, two points determines or defines one unique line.
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No. Two points determine one line, and only one.
No. A tangent touches the circle at exactly one point. A line that intersects a circle at exactly two points is a secant.
In classical or Euclidean plane geometry two points defines exactly one line. On a sphere two points can define infinitely many lines only one of which will represent the shortest distance between the points. On other curved surfaces, or in non-Euclidean geometries, the number of lines determined by two points can vary. Even in the Euclidean plane, two points determine infinitely many lines that are not straight!
secant
Unique line assumption. There is exactly one line passing through two distinct points.