define 2e-10?

In Excel HELP:
Lookup: "exponential notation" -->
Available number formats:

Scientific

This format displays a number in exponential notation, replacing part of the number with E+n, where E (which stands for Exponent) multiplies the preceding number by 10 to the nth power. For example, a 2-decimal Scientific format displays 12345678901 as 1.23E+10, which is 1.23 times 10 to the 10th power. You can specify the number of decimal places that you want to use.

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2e-10 ---> 2 X 10^-10 = 2 ÷ 10¹⁰ = 0.0000000002