What does the word by mean?

Usage examples for by

  1. And what do you mean by a 'daylight person'?" – Jan and Her Job by L. Allen Harker
  2. I wonder, by the way, if it was all taken. – At the Time Appointed by A. Maynard Barbour
  3. By the way, where did you say this prince man is? – Romance Island by Zona Gale