GM is the abbreviation of Good Morning, which means "good morning". In the currency circle (especially On platforms such as Twitter and Discord), it is often used as a friendly greeting at the start of the day.
GN is the abbreviation of Good Night, which means "good night". Similar to GM (Good Morning), it is used as the end of the day in the currency circle. Farewell greetings, probably means: I am going offline.
GM/GN does not have a specific meaning related to crypto or blockchain technology, but it is part of the online terminology of these communities. The use of these words highlights the 24/7 nature of the crypto market, with participants from around the world active at all times, coming online and offline at different times.