A multivariate random variable or random vector is a vector X=(X1,...,Xn) whose components are random variables on the same probability space (Ω, P). Every such random vector gives rise to a probability measure on Rn with the Borel algebra as underlying sigma-algebra. This measure is also known as the joint distribution of the random vector. The distributions of each of the component random variables Xi are called marginal distributions.
... out with 20.5% under the age of 18, 6.1% from 18 to 24, 24.6% from 25 to 44, 28.2% from 45 to 64, and 20.7% who are 65 years of age or older. The median age is 44 years. ...