What is EPS warning?

Excuse me, could you clarify what exactly an EPS warning is? I'm familiar with terms like "earnings per share" in finance, but EPS warning is somewhat new to me. Is it related to the company's earnings forecasts not meeting expectations? If so, how does it affect investors and the market in general? Is there a specific protocol companies follow when issuing such warnings? Lastly, what should investors do in response to an EPS warning?