Naturalness is the property that all parameters (that are pure numbers) appearing in a theory take values of order 1 (that is, 2.34 rather than 234000). The requirement that satisfactory theories should be "natural" in this sense is a current of thought initiated around the 1960s in particle physics, and is an aesthetic criterion not always compatible with Occam's razor, since many instances of "natural" theories have more parameters than "fine-tuned" theories such as the Standard Model.