Venting is a cathartic tactic for blowing off steam. It is a sharing of your emotions around a subject. “I feel so frustrated when that happened.” Venting can help you move forward or at least through the situation.
On the other hand, complaining is wallowing. It is coming from a place of powerlessness, victimhood. It’s not productive. “I hate working there. Everyone is so stupid.”
Venting can be helpful, especially if you tell your spouse that is what you are doing. Complaining is just draining to the listener.
If your spouse is complaining, validate them. That’s all they want. No need to ask further questions to extend the conversation. Don’t offer solutions or advice, they just want to complain. Just validate and try to change the subject. “That’s awful that it didn’t work out how you had envisioned. What are our plans for next week?”
Caveat: You know your spouse, and if they are venting or complaining, in the right setting, you might ask, “Are you venting or complaining? What do you need from me right now?”