In here, https://en.wikipedia.org/wiki/Degrees_of_freedom_(mechanics),
the degree of freedom is defined as "the number of independent parameters that define its configuration." So, if $N$ particles are in the system, the degree of freedom is $3N$.

But here, https://en.wikipedia.org/wiki/Degrees_of_freedom_(physics_and_chemistry),
defined as "The set of all dimensions of a system is known as a phase space, and degrees of freedom are sometimes referred to as its dimensions." In this sense, the degree of freedom is $6N$.

What is the definition of the degree of freedom?