The term 'WATCHFUL PERIOD' can be summarized as a period of vigilance or alertness, which is represented by the crossword solution 'VIGIL' (5 letters). This term is often used to describe a period of time when one is actively monitoring a situation or environment for potential danger or risk. It is also used to refer to a period of time when one is paying close attention to their surroundings in order to detect any changes or potential threats.