1. warn somebody about something that you think may or will happen
give a heads-up about what to expect
When you give somebody advanced notice of something, you give them 'a heads-up, particularly if it relates to something that could cause that person difficulty or trouble. It is typically used in a positive sense as telling somebody to be alert or to prepare for something is essentially doing them a favour, occasionally even at your own risk. This expression is common in both a social and professional context, and is similar to the phrases 'word to the wise,' and 'tip-off.'