Objective is that on which ALL observers would agree independently - without communicating. Picture a nucleus and electrons, with the nucleus representing a true, real, objective fact, and the cloud of electrons are things that would be affected by it even if each experienced the nucleus alone.
Subjective is that on which universal agreement requires communication. I sometimes like to call it "illusion" or, if shared thanks entirely to direct or indirect interaction between the perceivers, a "construct."
Reason being a sort of communication with oneself as talker and listener in the same head, rational beings (ie humans) are naturally very, very bad at determining what's objectively real. We can hope to arrive at objective truth (yes, I think it conceivably exists) only by trying very hard to resist biases. For example, we can try to overcome confirmation bias by eagerly seeking to prove oneself wrong - I desire to be right in saying "I'm wrong."
An example: I am watching an ant. I perceive an obstruction just ahead in its path. I tell myself the rock maybe doesn't really, objectively exist (to avoid any indirect or telepathic suggestion that might affect the ant). The ant stops at the rock, then goes around it. I think, "aha! the ant and I both agreed on the existence of the rock." But wait, was the ant real? Did it really go around the rock? Or am I just dreaming?... Look for other things that were or weren't but should've been affected by its presence or movement... I keep looking for clues until finally I say "Well, that's good enough for me to confidently say it is real."
The idea that everything is subjective simply because no two perspectives are the same is the equivalent of a mental shrug. The more things I can observe being affected by the rock - independently - the greater the probability of its objective existence.
It doesn't have to be a physical, material thing. Any idea on which completely independent agreement is conceivable is potentially an objective statement. Free will? I intentionally wave my arm; I ask my wife "did I just do anything?" "Yeah, you moved your arm." The kids agree. The dog perked up in reaction to my movement. a sheet of paper fluttered on the desk because I disturbed the air. All that goes in the right direction. Free will. Whew. I'm still not certain, but reassured.
Just because we have trouble perceiving objective reality doesn't mean it doesn't exist. I think we should just admit humans can't, alone or between themselves, be relied upon for objectivity. That's why I like to let plants and insects disprove the ideas I get.
Edited to be more objective