The caret (^) is used in several programming languages (as well as many graphing calculators, TeX and Microsoft Excel macros) to indicate a power, and some engineers or developers will use this convention in ordinary prose. Exponentiation is usually represented with superscripts, but the correct orthography is sometimes difficult or impossible to produce. Thus, ^5 indicates to the fifth power, which would ordinarily be set as superscript 5 (x⁵).
More broadly, the amount is expressed in expressed in scientific notation, in which values are expressed as multiples of a power of ten. This system makes it easier to represent very large or very small numbers and for people to comprehend their magnitude— most people would need to take some time to figure out which is the greater of 0.0000000825943201 and 0.00000000473201, for example, or to determine that the latter number is equivalent to 473,201 hundred-trillionths.
Thus, 1 part in 2x10^5 is equivalent to 1 part in 2 × 10⁵ or 1 part in 200,000, or 0.000005 (or 0.0005% as IanF1 notes). By the same token, 8x10^(-8) rad is equivalent to 8×10⁻⁸ or 0.00000008 radians.