Yes, hot springs and onsen are essentially the same thing. In Japan, the term "onsen" refers to hot springs, and these are natural geothermally heated springs that contain mineral-rich water. Onsen are popular in Japan for relaxation and health benefits. The water in these springs is often believed to have various therapeutic properties due to the minerals it contains.
So, when you hear about hot springs in Japan, they are typically referred to as "onsen." The terms can be used interchangeably when talking about the traditional Japanese hot spring baths.