What's the meaning of the letter ‘v’ in setvbuf()?

Question

Recently, I found two functions setbuf() and setvbuf() can be used to set stream buffer. What's the meaning of the letter v in the name setvbuf? Is it various, version or something else?

Answer 1

I didn't found any explanation of 'v' anywhere but I guess it may be 'variable' since it allows to specify the size and mode of the buffer.