You were in a meeting at work where you heard about a change in your work schedule. You're talking to an employee who wasn't at the meeting. You want to talk to her about the schedule change, but you're not ready to discuss it yet. You say to her:
Just a heads up - we're going to have to meet soon.
This is a phrase that you say before warning someone of something.
The phrase "Heads up!" comes from sports. You say this before throwing a ball to someone to let them know to raise their head and look for the ball, so they don't get hit. This phrase has spread to business and social situations as well, in the form "(this is) just a heads up".
This phrase explains is used to talk about something that you don't have to do now, but you predict that you will have to do it some time in the future.
This is a common phrase for indicating the topic of a meeting. For example, a parent can write a note to her son's teacher saying:
I'd like to meet to discuss my son's performance in your class and what I can do to help him do better.
Use "in" to express a schedule change:
There's been a change in today's schedule.
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