A future event is up in the air if it's not definite or if something about it (the time, the place) is not certain. For example, if you're planning a party, but you're not sure if it's going to happen for some reason, you can say, "The party is up in the air right now. We'd like to have it, but we're not sure yet if anybody will come." If the party is definite for Friday at 8p.m., but it's not clear yet whether it will occur at John's house or Ted's apartment, you can say, "We're definitely having the party at 8, but the venue is still up in the air."
A: So, I hear you're going to Italy for the summer.
B: Oh, that's now up in the air. I just got an internship at a magazine that I really want to work for, so now I'm thinking of canceling my trip to Italy.
A: Oh, that's a tough decision. I don't know if I would cancel a trip to Italy, though.
B: I know, but I can't say no to the internship. By the way, congratulations on your engagement.
B: I hear the wedding's in September.
A: Actually, that's up in the air, as well. Tara's sister is overseas right now and can't get back until next year, so we're thinking of moving the date to next summer.
B: But that's not so bad, right?
A: No, it's not a big deal. We've been together for five years, so we can definitely wait another six months or so.
venue - place for an event
overseas - abroad
or so - approximately, about
Alright everyone, what is up in the air in your life right now? Is it going back to your country, starting school, getting married, moving to a new apartment, ... Think about it, then try to incorporate the phrase in your conversations today.