I’m assuming you’re not looking for the chemical definition, referring to carbon based compounds. Organic is a designation referring to a few different things.

As a label coming from the USDA, organic refers to any product that has been certified as not growing in soil polluted with prohibited substances/compounds from at least three years prior to the harvesting of said product.

As a more general term, the term “organic” is used to denote that the production of the food is guided by standards geared towards conservation and preservation of biodiversity.

For livestock, organic means that the livestock in question had regular access to pastures. Additionally, they cannot be raised on a routine of growth hormones and antibiotics.

Exact definitions and terms vary from country to country, depending in large part on what body gives the organic designation to the product in question.