Meaning of the word "red flag" in English

What does "red flag" mean in English? Explore the meaning, pronunciation, and specific usage of this word with Lingoland.

red flag

US /ˈrɛd ˌflæɡ/
UK /ˈrɛd ˌflæɡ/

Noun

a warning signal or sign that something is wrong or problematic

Example:
His constant excuses were a major red flag for me.
Lack of transparency is often a red flag in business dealings.