What's it mean when someone says "intonation" in the context of a fretless? I think I understand the term in the context of string length and how to adjust it (open vs 12'th fret), but not the fretless usage.

In a nut shell, intonation as it would apply to fretless is accurately producing the note you are trying to play. (There's a lot of room for error)

What's it mean when someone says "intonation" in the context of a fretless? I think I understand the term in the context of string length and how to adjust it (open vs 12'th fret), but not the fretless usage.

Or are you talking about 'intonate'... in other words ajusting the bridge. In fretless usage you still need to set the bridge saddle so that the marking on the bass at the octave is really the octave. Sure you have the ability to move your left hand to bring the pitch in tune if you need to, but why make more work for yourself? Consistancy is the rule to playing in tune with a fretless instrument.

I would assume that he is talking about intonation in terms of playing the relative notes accurately in pitch. I don't think it's a question about setup at all.

To answer, intonation on frettless in terms of playing refers to the accuracy of the notes compared to the intonation system you are using. To simplify that, it means if, for example, a fretted instrument was playing the note C that your finger was in the correct spot relative to that fixed note and not sharp or flat.

OR if you have uncanny violin-like capabilities and can tune each note harmonically to the root of the chord.

but yea in a nutshell its how close you are to the relative note on a fretted bass