Meaning
An advance notification, warning, or casual alert about something that is about to happen.
Three examples from work
Deployment warning
DevOpsQuick heads-up: we are restarting the staging database in ten minutes.
DevThanks for the heads-up; I'll pause running my test suite.
Client schedule
Account ManagerJust a heads-up: the client's VP of Engineering will join tomorrow's demo call.
PMGood to know; we'll prepare a high-level architectural slide.
Capacity alert
LeadGiving the team a heads-up that next sprint will focus heavily on security compliance.
DevUnderstood, I will close remaining UI tickets this week.
Use 'give someone a heads-up' or 'thanks for the heads-up'. A friendly, polite way to keep teammates prepared without sounding alarmist.