To add a little to Marcus's solution, it's scientific notation, 'e' is basically 'times 10 to the power of' so in this case, it's 1.0 times 10^(-5).

(This next part is just an educated guess)

Epsilon is sometimes used in mathematics to represent a minimal change from one number to another (e.g. 1 + epsilon is just a tiny bit above 1), but since computers are discrete I'm guessing 1.0e-5 has just been arbitrarily chosen as a small value that will behave similar to epsilon in mathematics, but for discrete values.

It's really hard to tell you more without some context. We don't know what the rest of the code looks like.

you have a readonly property in stead of a const or something like that.