This code is storing the stage name in string format but one of the value contain &
and because of it it showing &
by replacing the string value
string stages = ''; //string type stages variable
for (string s :stagenames ){ //loop
stages = +stages+s+':'; //assigning value to the stages
System.debug(stages.unescapeHTML4()); //getting all the values inside it one by one
}//but one string is jack & Jill so instead of showing actual string it just showed me 'jack &'