The term "bunk" has several meanings, depending on its context.
1) In a general sense, it can refer to something that is false or untrue; an unfounded belief or idea. For example, "That's just bunk - there's no scientific evidence to support that claim."
2) It can also be used as a term for a bed, particularly in a military or institutional setting. In this sense, it refers to the type of bed and not its quality. For instance, "I had to sleep on bunks in the army barracks."
3) Finally, "bunk" can refer to a nonsensical or foolish conversation or activity; something that is considered pointless or unimportant. An example usage would be: "We spent hours talking about nothing but bunk - it was such a waste of time!"