what does this mean: e-9

I think the use of E to denote exponent began in ancient times when cavemen used to program computers using the FORTRAN computing language using punched tape or punched cards.  There was a fixed limit to the number of characters that could be punched on a line of coding (∼60 I think) so anything to save space was useful, and E rather than *10^ saved a few characters.  

The E was used where single-precision calculations were required; the letter D was used to mean the same thing for double-precision calculations.

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It's a shorthand way to write  x $${{\mathtt{10}}}^{-{\mathtt{9}}}$$

e.g., 0.04 can be written 4e-2

It's called scientific notation.

This is probably true BUT  I would like to know why e is used for scientific notation when e has a meaning all of its own.  I find it very confusing.  

CAN SOMEONE PLEASE EXPLAIN TO ME THE LOGIC THAT HIDES BEHIND THIS SEEMINGLY SENSELESS LETTER ALLOCATION?

e is shorthand, it signifies the exponent when the multiplier is written as a power of 10

I have the feeling it started off being a capital E (probably to appease the purists and critics, not looking at anyone) but out of expediency and usage evolved into the lower case. The lower case e stands out better, being a short character among greater height digits. The upper case E more easily hides. In practice, it is nigh impossible to confuse this e with the constant―the digits that follow the exponent e are never superscripts. That's just my thoughts, no cites to back me up.

I find it confusing, but then I find everything confusing.

I can only imagine the logic in the real world and the logic in the imaginary world is not real to me at all.