The carpel is a unit of the gynoecium consisting of ovary, style and stigma:
Stigma: the area at the distal end of the style that is usually sticky so that it can capture pollen grains.
Style: After capture compatible pollen grains germinate and the pollen tube grows down the style transporting the generative nuclei towards the ovary.
Ovary: usually swollen basal part of the carpel that houses the ovules (become seeds after fertilisation) that are located within a cavity called the loculus (also known as a locule). In the plural form these words are loculi and locules, respectively.
Illustration from Clarke, I. & Lee, H. (2003) Name that Flower, Melbourne University Press, Victoria.