Basically what that does is take a variable that has been defined elsewhere and substitutes it into the statement. Assuming you are using Oracle, you can get a user input up front by using
ACCEPT Region PROMPT 'Enter region to be searched: '
or you can use a define statement to hard code it. Either way, once that variable is defined you can then use it by typing &Region
. If someone types in "South" for example, then the compiler would see this as equivalent to
Where substr(hou.name,1,2) like 'South%'
And would thus give back results like South Carolina, South Dakota, etc.