Chiptune music is not a genre - it interprets many genres and is an instrument for many types of music - and nor do chiptunes have a narrow type of sound as you'll discover from these examples.
The description "8-bit music" is somewhat misleading because an 8-bit computer may have an 8-bit central processor while also having other capabilities and components (memory, sample size, etc.) that deal in more or less than 8-bits. Moreover, 16-bit era video game music, such as that released on the 16-bit SEGA Genesis (1988) or Super Nintendo (1990) is also regularly included in the chip music category.
Rather than a specific number of bits or genre type, chip music is defined by the hardware limitations and creative techniques that characterize sound and music composition on early game consoles and home computers.