Given: 8.6e12 This is a scientific notation, and usually called E-notation.
In the given expression, "8.6" is called significand* that adds preciseness to the number. Significand is a real number.
"e" is interpreted as (8.6) "times 10 raised to the power of" (12). Notice that "e" is not the base of natural logarithm (≈2.71828...), but means base-10 instead. Upper case "E" is also used in place of lower case "e" to avoid confusion.
"12" is the exponent. Exponent is an integer. Thus, this expression is a shorter form of base-10 expression: 8x10^12.**
Therefore, the answer is: 8.6e12=8.6x10^12 (eight billion,six hundred million).
* In other number systems given in forms such as 2x8^5, 5x10^6,or Bx16^7, all 2, 5 and B are called the sinificand as well.
** This kind of shortest expressions of numbers are widely used to program soft wares for computers or calculators. Because those programs present or process big quanties of very large or very small numbers. The shorter the better.