apple corer [ap–uhl kawr-er, kohr-] noun
A hand tool that easily removes the core (with seeds) from the apple. The open end of the cylindrical tool is placed over the apple’s center, inserted and twisted to remove the core, ready to be sliced, diced. An apple corer can be used for pears as well.
This picture below is of a Cuisipro apple corer, which improves upon the typical tool by adding a mechanism to help release the core after it is removed.