That's a great question. The observable universe is the region of space that humans can actually or theoretically observe with the aid of technology, because the electromagnetic radiation from these objects has had time to reach Earth since the beginning of the cosmological expansion. The observable universe is different from the entire universe, which is possibly infinite and without spatial edges.
The observable universe is approximately 93 billion light-years in diameter. This number is derived from several considerations, such as the age of the universe, the speed of light, and the expansion of space. The observable universe can be thought of as a sphere that extends outwards from any observation point for 46.5 billion light-years, going farther back in time and more redshifted the more distant away one looks.
The word observable in this sense does not refer to the capability of modern technology to detect light or other information from an object, or whether there is anything to be detected. It refers to the physical limit created by the speed of light itself. No signal can travel faster than light, hence there is a maximum distance (called the particle horizon) beyond which nothing can be detected, as the signals could not have reached us yet.
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