What are “select-by-word” characters?

Question

What are the "select-by-word" in gnome-terminal's preferences?

Answer 1

"Select-by-word" characters are those characters that define words. They are used to determine which characters to select when doing double clicks.

Eg., if you have a-z@ in this list, a valid word would be a@z. If you then have a string like

333a@z444

and you make a double click over 'a', '@', or 'z', it will only select a@z, because '3' and '4' aren't valid word characters.