The objective reality is the collection of things that we are sure exist independently of us. Every person is able, in principle, to verify every aspect of the objective reality. Anything that cannot be verified in this way is not part of the objective reality. The 20m tall ironbark tree in my neighbour's yard is part of the objective reality. It's presence can be verified by any person by simply looking at it, or a surveyor determining its position, by taking a photo of it etc. Moreover, the absence of the tree would imply that the tree does not belong to the objective reality.
Recall that the sensation of seeing the colour red lies in our subjective world. To make a direct comparison with the objective reality first note that the colour of light is related to the light's wavelength, i.e. the distance between adjacent waves that the light is made of. Now consider a device, called a spectroscope, for measuring the wavelength of light in terms of a small fraction of a metre. Such a device can be used to establish objectively that a beam of light is red based solely on the measured value of the wavelength. The wavelength value can be checked and verified (or otherwise) by any person. When technicians compare their measurements of the wavelength they are comparing elements of the objective reality and not sensory information.
We all have a vested interest in knowing what the objective reality is. For example, salespeople will tend to exaggerate the qualities of their wares, an air conditioner, say. But as a potential customer, we want to know what the objective qualities of the air conditioner really are. We may consult an independent review on the web or in a magazine to get this information.
Regardless of how hard we try to determine the constituents of the objective reality, the objective reality nevertheless rests on assumptions. Indeed, as noted above, it's very existence is assumed. Another assumption is that the objective reality has existed in the past and will continue to exist in the future. This assumption underlies the concept of time in the objective reality.
The objective reality is clearly an essential thing if we are to develop a meaningful perspective of the world. Nevertheless its very existence is assumed.
It takes quite a lot of effort to validate the elements of the objective reality. As a child we are taught many things are "real", and so implicitly belong to the objective reality, that later we realise are simply untrue. However some people appear not to know how to establish if something is part of the objective reality or not.
An example is given by water dowsing (or divining). There are people who believe that they can tell where water lies under the earth using a piece of wire or a forked branch. All such claims are easily testable by digging a hole where ever water is claimed to be or, just as importantly, where it is claimed not to be and recording the results. Unfortunately no claim of the ability to dowse for water has ever been verified in an objective manner. Of course there are stories by the believers of the practice of its success but whenever it is put to controlled testing the results are no better than random guessing. Yet people believe that the practice of water dowsing is valid. They include it as part of the objective reality.
Belief continues in the claims of mystics, fortune tellers, palm readers, astrologists, people with extra sensory perception and so on, as if the claims were part of the objective reality, but none of these things survive objective testing. Presumably these beliefs have qualities that give people hope, satisfaction or some other subjective merit. These believers lack the basic analytical skills that would allow them to distinguish between the subjective world and the objective reality.