Regex asterisk - match the previous element 0 or more times

let* will match:

le
let
lett
lettt

and so on.

So another way of saying this is that the * allows the previous element - t in this case, to be either omitted entirely or to appear once or multiple times.

Example:

$ grep 'let*' /etc/sane.d/escl.conf
/etc/sane.d/escl.conf:# by writing a complete URL and an optional model name.
/etc/sane.d/escl.conf:# Please report the devices having this problem on sane-devel