I'd define objective morality as something that is unchanging and etched into the laws of nature as it is with our ethics. For example, if you kick a ball it will move opposite to the direction you kicked it, there will never be a scenario where you kicked the ball and the ball didn't move, this is what I mean by objective, something that is unchanging.
Before we understand what objective morality is we have to understand what subjective morality is first. Subjective morality is morality that relies on interpretation: When it is said "You shall not kill" the meaning of it relies on your understanding, so you will be able to modify and twist it to your needs like "You shall not kill unless it is justified".
What objective morality is, is morality that does not rely on interpretation: When it is said "You shall not kill" it is objectively true and your interpretation must remain the same as the author decided. Objective morality is static and will not change, what is wrong will be wrong and what is right will be right so on and so fourth.
I personally don't believe in objective morality and think that morality along with culture in general changes and evolves depending on the circumstances and it is impossible to replicate the same interpretation to every human.
Although I am interested in learning about what other people think regarding this topic.