A carpel is the female reproductive organ of a flower. The parts of the carpel are:

• the stigma, a receptive (usually sticky) area to which pollen grains (male gametes) adhere once delivered there by a pollinating agent;
• the style, a stalk connecting the stigma with the ovary below; and
• the ovary (also also called a megasporophyll) containing the female reproductive cell or ovule.

A flower can have a single carpel, or several fused carpels (called a compound ovary). The carpel (if single) or carpels (whether fused or distinct) comprise the pistil or gynoecium of the flower. Fertilization of the ovule or ovules results in development of the carpel(s) into a fruit.

The gynoecium is the innermost whorl of the parts of a flower, and in many flowers the other parts (sepals, petals, and stamens) are attached to the receptacle beneath the gynoecium. In such cases, where the ovary lies above the attachments of the other distinct floral parts, the flower is described as having a superior ovary. In many species with a superior ovary, the other floral parts are fused to form a cup called a floral tube or calyx tube. In these flowers (examples include plum, cherry, and blackberry), the ovary lies physically lower than the lobes of the sepals and petals and below the point of attachment of the stamen filaments; however, the ovary is still considered to be superior.

In those flowers in which the floral tube is fused with the ovary, the sepals, petals, and stamens appear to grow out from the top of the ovary, and the flower is said to have an inferior ovary. Examples of plant families with inferior ovaries include orchid, sunflower, and cactus. The position of the ovary is an important consideration in the identification and classification of plant species, as well as the kind of fruit that develops.