A dimension is a coordinate in space. Thus, an -dimensional object is one that needs at minimum n coordinates to specify a point anywhere in it.
Reality has an absolutely infinite amount of dimensions and for all intents and purposes, it is more than enough for anything and everything to exist within its own right. Anything inaccessible through the concepts of dimensions is not considered part of this Reality, but other-Realmly.
While it is borderline impossible for humans to imagine anything remotely 4 dimensional, beings from the 4th dimension find 3rd dimensional life just as baffling. Same thing downwards; 0 dimensions may be the lowest dimension we can visualize through the normal concept of space, but not only is negative-dimensional space used in earthly science, but also is a real subsection of Reality, just not in the exact way we think.
It is currently unknown as to whether life can exist in every dimension, the only way to find out if a dimension can support life is to find a lifeform inside of said dimension, and this has been done for so many dimensions positive, negative, imaginary, complex, hypercomplex, , and more, that the number can not be accurately described using symbols, but is over in all cases. There is no known logical way to find out, so brute-forcing is required.