What is this apple's abnormality?
I take it that the question is about the mis-shapenness of the apple, that the stick we see in the dip is the core. The morphology (shape) of fruits such as apple and pear are very sensitive to how well the fruit was pollinated. As we know there can be a variable number of seeds in an apple, but the important fact determining shape is that there should be viable seed develop in each of the five seed pockets resulting in balanced development of the fruit. If the pollination is poor and only a few embryo seeds are fertilized, then the development of the surrounding flesh will favour the pockets that contain viable seed, resulting in possibly mis-shapen fruit. Once you have wondered enough and decide to eat, cut open carefully and on the small side you should see that the seeds are either too few, non-existent or failed to develop.