A black hole is a region where mass has been packed so densely that its gravitational pull becomes inescapable beyond a certain boundary, called the event horizon. Nothing that crosses that boundary, not gas, not light, not even information, can ever get back out.
Most black holes form when a massive star collapses at the end of its life, but far larger ones, called supermassive black holes, sit at the centers of most galaxies, including our own Milky Way, with masses millions or billions of times that of the sun.
Despite their name, black holes are not empty voids that swallow everything nearby indiscriminately, objects can safely orbit one at a distance, the same way planets orbit the sun. In 2019, the Event Horizon Telescope captured the first ever direct image of a black hole’s silhouette, confirming decades of theoretical predictions with an actual picture.