The letters in any mathematical formula can stand for anything you
want them to. When a scientist writes a formula or equation with
variables in it, it's up to him to explain what each letter stands for.
When a formula becomes popular and widely known for a long time,
then often they stop explaining what the letters mean, since everybody
has already seen it so many times.
That's the case with this one. It's widely recognized as one of the fall-outs
from Einstein's work in Relativity theory. In that case . . .
'E' stands for energy
'M' stands for mass
'C' stands for the speed of light.
and the formula says that the energy in a piece of mass is equal to the
mass multiplied by the square of the speed of light.
That's what they mean IF this is Einstein's famous formula. But it doesn't
necessarily have to be that. It could be the equation that tells you the total
area of a quilt.
'E' = the total area
'M' = the number of squares in the quilt
'C' = the length of each side of each little square.
Whoever writes the equation has to tell you where it comes from, so that
you have some notion of what the letters in it mean.
