Regex is a regular expression for example disecting parts of text from a bigger collection of text.
Say for example that you want to find all names in a newspaper. Instead of reading the entire thing looking for each name you can make a regex model of finding every word starting with a capital letter that is not right after a punctuation.
In your example the regex ^ means it looks for something that starts with the following:
– A small or capital letter between a to z
– The word is to letters long
Read a couple of examples and you’ll get the hang of it.
It is simply just a model how text is built up.