PrtScn Key for Screen Capture
Windows's PrtScn/SysRq for Screenshot
On today's PC keyboard, you'll find quite a few relic keys. PrintScreen/SysRq, ScrollLock, Pause/Break, Insert. They used to have meaningful purposes in the 1980 or earlier, some of them are separate keys. But computer hardware changes, and software changes, dramatically over the past 20 years. Keyboard itself did not change as fast, due to habit. So, these keys became defunct.
Because the name “Print Screen” somewhat relates to screen capture, so Microsoft have chosen it to be the key for saving screenshots. Similarly, the Backspace ⌫ key, was chosen as the key for web browser to go BACK to previous page. Note that this key is labeled “Delete” on Apple's keyboards, even they sent the exact same signal. In Apple's operating system, in Mac Classic of the 1990s or Mac OS X since early 2000s, this key was not used for browser's back function, only so around ~2006 when Apple started to adopt many Windows's conventions.