noun: (informal) A period of time in the life of dogs, defined such that the average life expectancy of a dog in "dog years" is numerically equivalent to the average life expectancy of a human. A 4- and a 5-year-old dog are about as mature as a human of 28 to 30 years and 33 to 35 years, respectively. The most common calcuation uses a ratio of seven dog years to one human year.
noun: A unit of age relative to the species being considered, defined such that an animal's age in "dog years" is the equivalent age of a dog in calendar years.
