What does 4 days of LH surge mean?

An LH surge, also known as a luteinizing hormone surge, is a rapid increase in the levels of LH in the bloodstream.

When the LH surge occurs, it will help in promoting ovulation within 36 hours (2 days). So this means ovulation most likely occurred about two days (48hrs) after it first started in this case the LH surge lasted for more than four days.