A jar is a rigid, approximately cylindrical container with a wide mouth or opening. Jars are typically made of glass, ceramic, or plastic. They are used for foods, cosmetics, medications, and chemicals that are relatively thick or viscous: pourable liquids are more often packaged in a bottle. They are also used for items too large to be removed from a narrow neck bottle.

In software, JAR (Java Archive) is a package file format typically used to aggregate many Java class files and associated metadata and resources (text, images, etc.) into one file to distribute application software or libraries on the Java platform.

A jar is a large, approximately cylindrical container made of glass, clay, or plastic.

• Bell jar, a piece of laboratory equipment used to contain a vacuum
• Cookie jar, a jar used specifically to store edible treats such as cookies or biscuits
• Killing jar, a device used by entomologists to kill captured insects
• Kilner jar, another type of jar for storing foods
• Leyden jar, a simple capacitor
• Mason jar, a jar used to preserve various foods (e.g. fruit, jam, vegetables)
• Specimen jar, an instrument used in anatomy to preserve anatomical specimens