What does “au cas où” mean in French?

“Au cas où” means “just in case.” You can end a sentence with it and say nothing more. “J’ai pris un parapluie, au cas où” = “I took an umbrella, just in case.” The rest stays unsaid. When you do add a reason, French uses the conditional: “au cas où il pleuvrait” = in case it rains. Short, very common in daily speech, and with a small grammar twist worth knowing.

The whole clip turns on this phrase. He has filled an online cart with 250 euros of clothes but has no money to pay. She asks why he made the cart. He shrugs: “C’est au cas où” — “It’s just in case.” She presses: “Au cas où de quoi ?” (“Just in case what?”). His answer: in six months, if he has the money, “paf, je peux faire la commande” — “boom, I can place the order.” “Au cas où” breaks into au (at/in the) + cas (case) + où (where). You use it two ways. Alone at the end of a sentence, as in the clip, it means “you never know.” With a full clause after it, French uses the conditional tense: “Je te laisse mon numéro, au cas où tu en aurais besoin” = “I’ll leave you my number, in case you need it.” French uses the conditional here, not the subjunctive. This surprises learners who know Spanish or Italian, which use the subjunctive in the same situation. Two more quick examples: “Prends un manteau, au cas où” (Take a coat, just in case). “Au cas où il serait absent, appelle-moi” (In case he is away, call me). The standalone use is the form you will hear most in everyday speech.