What is "dog year"

n. 1 (context informal English) 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. 2 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.