Semicolon in SELECT query
This is just concatenating a semicolon between two fields. Think of it like selecting LNAME + ', ' + FNAME or something similar.

It's generally fine to have presentation layer items like this in the select list, but it's important to avoid them as predicates (anything in a join or where clause), because in SQL Server, they're not SARGable.

SQL Server uses +, which is different from other platforms, that may use || to concatenate things, which is an issue I've written about in the past.