**Linear separable **means that there is a hyperplane

This means that there is a hyperplane, which splits your input data into two half-spaces such that all points of the first class should be in one half-space and other points of the second class should be in the other half-space.

**In two dimensional space,** it means that there is a line, which separates points of one class from points of the other class.

**For example**: In the following image, if blue circles represent points from one class and red circles represent points from the other class, then these points are linearly separable.

**In three dimensions,** it means that there is a plane that separates points of one class from points of the other class.

Hope this answer helps.

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