Meaning of the phrase "dipole moment of the combination" Here is a question I came across in a book: 

Three point charges $-q$,$-q$ and $2q$ are placed on the vertices of an equilateral triangle of side length $d$ units.What is the dipole moment of the combination?

I had learnt that the dipole moment is defined for 2 point charges only with equal magnitudes but opposite character.I am in a bit of a fix regarding what the author means by that phrase in bold.Thank you in advance!
Edit:I just noticed theoretical physics has been merged here;I sincerely apologise if the question is unbearably stupid.
 A: Dipole moment is a vector and can be calculated using formula
$$\vec{p} = \sum_i q_i \vec{r}_i.$$
It can be shown easily using the formula above that in case of two charges separated by distance $d$
$$\vec{p} = q \vec{d},$$
where vector $\vec{d}$ goes starts at negative ends at positive charge.
http://en.wikipedia.org/wiki/Electric_dipole_moment#Dipole_moment_density_and_polarization_density
A: 
I had learnt that the dipole moment is defined for 2 point charges only with equal magnitudes but opposite character.

Actually, that is not the case. You can calculate a dipole moment for any charge distribution.
In fact, the dipole moment is just one of a whole series of multipole moments which can be used to describe a charge distribution.


*

*The monopole moment $$q = \sum_i q_i$$

*The dipole moment $$\vec{p} = \sum_i q_i \vec{r}_i$$

*The quadrupole moment $$\overset{\leftrightarrow}{Q} = \sum_i q_i(3 \vec{r}_i \otimes \vec{r}_i - r_i^2)$$


and so on. These moments are kind of analogous to the coefficients of a Taylor series expansion.
It turns out that if you take a positive point charge and a negative point charge of equal magnitude and bring them infinitesimally close together, then the resulting charge distribution (called a dipole) has only a dipole moment. All the other multipole moments are zero. That's where the dipole moment gets its name. You've been taught that you can calculate a dipole moment for a system of two charges because that is the simplest way to create a charge distribution with a dipole moment. But it is not the only way.
