e = exponential. Its a mathmatical term.
For example, Int 64 = -9.2e18 to 9.2e18 is the same as saying -9.2 * 10^18 to 9.2 * 10^18.
(^ means to the power of by the way).
Also, for example 9*10e2 would be the same as 9*100.
This is done as numbers like 10^18 are really long (1000000000000000000) and much harder to read than e18. They are also a lot more easier to understand while doing calculations and reading books.
You'll do it in GCSE Maths, and if not definitely at A Level.
Hope that helps
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