Can anyone explain to me in simple English words the meaning of this regex

1 

let sampleWord = "astronaut";
let pwRegex = /^\D(?=\w{5,})(?=\w*\d{2,})/;
let result = pwRegex.test(sampleWord);
2

^ first character \D should not be a number
(?= in the tested string \w{5,}) should be 5 or more consecutive word characters
(?= in the tested string \w* should be zero or more consecutive word characters \d{2,}) followed by 2 or more consecutive numbers

word characters = alphanumeric (a-z 0-9) and underscore _

PS: https://regexr.com is a great tool for that. If you hover over some entered regex it explains each part to you.

3

A tool you may get a lot of use out of:
Regex101 will give an explanation of all the parts of your regular expression. (It also allows you to write tests for your regex, etc).
screenshot