Half-space may refer to:

• Half-space (geometry), either of the two parts into which a plane divides Euclidean space
• Half-space (punctuation), a spacing character half the width of a regular space
• (Poincaré) Half-space model, a model of 3-dimensional hyperbolic geometry or higher-dimensional hyperbolic geometry using a Euclidean half-space
• Half-space model (oceanography), an estimate for seabed height in areas without significant subduction
• Siegel upper half-space, a set of complex matrices with positive definite imaginary part

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