A linga, sometimes referred to as lingam or Shiva linga, is an abstract or aniconic representation of the Hindu god Shiva in Shaivism. Here are some key things to know about lingas:

• Etymology: The word linga means "sign, symbol or mark" in Sanskrit.

• Representation of Shiva: Lingas are typically the primary murti or devotional image in Hindu temples dedicated to Shiva. They are revered as an emblem of generative power and symbolize the god Shiva.

• Form: Lingas are smooth cylindrical masses, often resting in the center of a lipped, disk-shaped object called the yoni, which is an emblem of the goddess Shakti. They can be made of stone, metal, wood, clay, sand, or gems. Some lingas are self-created or svayambhu-lingas, formed naturally from rock or ice. Others are pratishtith-lingas, carved out of rock, wood, or gems, or molded out of clay, sand, or metal. Some lingas are covered by a metal sheath and given a face so that the devotee can relate better.

• Meaning: The symbol of the linga can be understood from three different perspectives: as a material object in the external world, as a means of moving from the external to the internal, and as the Light itself. The image of a linga points to the unmanifest, causal principle contained in the object. Lingas represent the productive and creative principle of nature as embodied in Shiva.

• History: Archeological finds from the Indus Valley civilization suggest that lingas have been in use for thousands of years. The earliest known Shiva lingam is the Gudimallam lingam from the 3rd century BCE.

In summary, a linga is an abstract or aniconic representation of the Hindu god Shiva in Shaivism, typically found in Hindu temples dedicated to Shiva. It is a symbol of generative power and can be made of various materials. The symbol of the linga can be understood from different perspectives and represents the productive and creative principle of nature as embodied in Shiva.