What does it mean when a dot appears in a logic gate other than the NOT gate? (in logic diagrams)
This is a NOR gate. You can implement a NOR gate using a combination of a OR and a NOT gate. However, in MOSFET implementation or other technologies (i.e. electrical hardware architecture), we can build a NOR gate directly and more efficiently (i.e. more efficient than using a OR and a NOT gate). That's why we use NOR as well.