According to the International Softball Federation, a bye is the following:"When because of withdrawal/s there are an uneven number of teams in sections (e.g. seven (7) teams in one section, eight (8) teams in the other section), the section with the least number of teams shall be considered to have a bye and each team in that section shall be awarded one (1) win."
I found this on page 5 of the ISF TECHNICAL & VENUE MANUAL FOR OLYMPIC, WORLD CHAMPIONSHIPS, REGIONAL AND MULTI-SPORT COMPETITIONS.