Hard or "hardness" may refer to:

• Hardness, resistance of physical materials to change under force
• Hard water, water with a high mineral content
• Mathematical difficulty; see computational complexity theory
• A difficulty level in a video game
• Street hardness, an attribute characterized by physical and mental toughness due to living in hostile urban environments
• Hard, Austria, a town in Austria
• Slang for erection of the penis when sexually excited or aroused. See Erection
• Hard (Brainpower album), a music album by Brainpower
• Hard (Gang of Four album), an album by Gang of Four
• Hard (Zürich), a quarter in Zürich
• Hard (band), a Hungarian hard rock supergroup
• Hard (Jagged Edge album)
• Hard (tennis), a type of tennis court

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