Common confusion
Why people say offside anyway
People sometimes use "offside" as shorthand when a player looks too far forward, too close to the net, or out of their starting slot. That wording is misleading. Volleyball calls these situations position faults, overlap faults, attack faults, block faults, or center-line faults depending on what actually happened.
Edge case
A back-row player is ahead of front-row teammates
That can be a fault at service contact if the required front-back relationship is broken. Once the serve is contacted, the same player may move forward, set, defend, or prepare an attack, but back-row attack and blocking restrictions still control what they may legally do at the net.