(They ain't perfect, of course.)
"In astronomy, declination (abbreviated dec; symbol δ) is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. The declination angle is measured north (positive) or south (negative) of the celestial equator, along the hour circle passing through the point in question."
Anyone who doesn't know what declination is, know from reading the introductory paragraph of this scientific Wikipedia article?
Anyone? no? :-)
I rest my case, m'lud.
On a celestial sphere (planet, star, etc) the declination angle (being 0 is at the equator, being 90 degrees is the north pole of the sphere, being -90 degrees, is at the south pole).
You also need another angle known as the "hour angle" to locate a point on the sphere. It doesn't explain what that is, but as can be seen on Wikipedia, you can easily click on that word to go to the entire page that explains what it is.
What don't you understand?
Why should this be a metric one would want Wikipedia to meet? It's an encyclopedia, not an astronomy course.
Of course, the brilliance of Wikipedia is that if you think you can write a clearer intro, you can do so! You could even add it to the simple language version of the page - https://simple.wikipedia.org/wiki/Declination