From dictionary.com:
Note: The term is especially applied to fireballs, and the masses of stone or other substances which sometimes fall to the earth; also to shooting stars and to ignes fatui. Meteors are often classed as: aerial meteors, winds, tornadoes, etc.; aqueous meteors, rain, hail, snow, dew, etc.; luminous meteors, rainbows, halos, etc.; and igneous meteors, lightning, shooting stars, and the like.

usage   The senses shown above are the chief living senses of fulsome. Sense 2, which was a generalized term of disparagement in the late 17th century, is the least common of these. Fulsome became a point of dispute when sense 1, thought to be obsolete in the 19th century, began to be revived in the 20th. The dispute was exacerbated by the fact that the large dictionaries of the first half of the century missed the beginnings of the revival. Sense 1 has not only been revived but has spread in its application and continues to do so. The chief danger for the user of fulsome is ambiguity. Unless the context is made very clear, the reader or hearer cannot be sure whether such an expression as "fulsome praise" is meant in sense 1b or in sense 4.

[From Latin tangent-, tangens, present participle of tangere (to touch).]

The word tangential has numerous cousins, words derived from the same root: tax, contact, attain, intact, tact, taste, tangible, tactile. What an unlikely bunch of words to come out of the same parent! What's common in all is the idea of touching (or not, as in case of "intact"). -Anu

Function: transitive verb

Imagine a plane, and a vector normal (perpendicular) to the plane.

Let's say we have a vector v:

v = v1(x) + v2(y) + v3(z), sometimes written as <v1, v2, v3>

Imagine a point P1 some shortest distance d from the plane, in the direction of the vector. In other words, you could use some other vector than v to get from P1 to the plane, but unless that other vector is parallel to v, you'll end up traveling a greater distance than d before you get to the plane. Again: P1 is distance d from the closest point on the plane, and you'd move in the direction of vector v to get from that point on the plane to P1.

Now imagine another point P2 on the other side of the plane — it's like a reflection of P1. Both points lie along the direction of the vector - if you start at one of the points, and move in the direction of the vector (or 180 degrees from the vector, depending on which point you started from), then you'll hit the other point. Both points are the same distance from the plane.

For convenience, let's assume that P1 and P2 are a single vector's length away from the plane, though it might be any non-zero multiple.

Ok, you can define the plane as the set of all points which are the same distance from both P1 and P2.

Now we define the two points:

Let x, y, and z represent the points on the plane. Since P1 and P2 are equidistant from the plane along a vector normal to the plane (i.e. if the plane were a mirror, the reflection of P1 would appear at P2), we can define the plane as being all those points which are the same distance from both P1 and P2:

Also, P2 + 2(v) = P1 (because P1 lay along the direction of the vector from the plane, and P2 is on the other side).

Square both sides:

Now we're going to expand each (x-a1)2 term into terms like this = x2 - 2*a1*x + a12:

And now we'll bring all of the variables over to the left, and all of the constants to the right:

Okay now, since P1 is two vector v's worth away from P2, then the vector

is going to be equivalent to 2v (two vector lengths).

That part on the right isn't important — it's just a number that shifts the origin of the plane around, without tilting it. Changing that right-hand stuff doesn't change the slope of the plane; it just moves it around to pass through another set of points, without rotating it, if you understand me. The important part of this exercise is that the stuff on the left ends up being the normal vector to the plane times x,y,z, so the equation for this plane (or any parallel plane) devolves into

where v1, v2, and v3 are the coordinates of the normal vector v.

So if someone asks you for the equation of a plane that is normal to vector <2, 3, 4> and which passes through point (-2, -1, 0), you just say:

Easy.