The word "reflection" comes from the Latin verb "reflectere," which itself is formed from the prefix "re-" (meaning "back") and the verb "flectere" (meaning "to bend"). This suggests that the original meaning of "reflection" was something that was bent back, like light reflecting off a mirror.
Over time, the meaning of "reflection" broadened to encompass other concepts, such as the act of thinking deeply about something or the image that is produced when light bounces off a surface.