...which means nothing to a person who doesn't know what it is.
And even if they have heard of it, trying to understand how it works can be tricky unless it's explained well... and I've seen a lot of textbooks that do a terrible job of making the reader UNDERSTAND the concept.
It's like college electronics and other engineering classes. The professor usually scribbles all kinds of cryptic looking equations on the board, the student scrambles to copy them into his notes, then the prof. asks "any questions?" and the student is so baffled by it all that he can't even think of WHAT to ask. OK, good, on to the next equation.....
I prefer to teach with diagrams, analogies and simple explanations FIRST and get the student to understand the concept, THEN present the math. That way, the student already understands and says "Ah ha! I see".
Imagine teaching a grade school kid "Y=MX+B". Call it a "first order linear equation". HUH? Talk about the slope and intercept. HUH? What is it even used for???
But, instead FIRST give some real world examples like "degrees C to degrees F conversion" and show how at 0 degrees C the F value is 32 and therefore there is an offset. Then show how degrees F climb up "faster" than degrees C (by drawing a little letter F climbing up a hill and a little letter C climbing up a shallower hill).
NOW, introduce "slope" (the hill) and "intercept" (the offset) and bingo! The light of understanding shines brightly.
There's nothing worse than a teacher that can't teach.