Soft, spongy tissue often found in the middle of plants or animals or the essence of something. It also refers to removing the pith from something, which is not necessarily the essence of how the word is used today.
Andrew Johnson is a New Zealander who has Parkinson's disease. You might not know it from looking at him, though. Johnson's doctors connected him with Deep Brain Stimulation (DBS), which has an incredible effect on the disease, as he demonstrates in a video:
VideoMedicineParkinson's DiseaseDeep Brain StimulationInstant effectsSenses of humor even in crisisDon't lose the remoteHow lucky we are to be alive right now