Revision 3 of 3, by Kai Burghardt on 10-16-2019. The page as it is now.

Plus

The symbol + (pronounced “plus”) is used to:

explicitly indicate the positive sign of a number,
add two numbers resulting to a number,
form a union of sets,
(FPC) concatenate two strings (or characters; except pchar).
if {$modeSwitch arrayOperators+} (default in {$mode Delphi}), concatenate arrays (since FPC 3.2.0)
enable a feature in a {$modeSwitch}

pascal

program plusDemo(input, output, stderr);
    
    var
        x: longint;
        g: set of (foo, bar);
        m: string;
    begin
        // unary operator: positive sign
        x := +7;                    // x becomes positive 7
        x := +$100;                 // x becomes 256
                                    // (dollar sign denotes hexadecimal base)
        
        // addition
        x := 7 + 7;                 // x becomes 14
        x := 7 + 7 + 7 + 7 + 7 + 7; // x becomes 42
        
        // union of sets
        g := [foo] + [bar];         // g becomes [foo, bar]
        
        // concatenation of strings and/or characters (FPC/Delphi extension)
        m := 'Hello ' + 'world!';   // m becomes 'Hello world!'
    end.

The plus sign is also a unary operator. One can write such stupid expressions as ++++++++++++++42 which will evaluate to positive 42.

In ASCII, the character code decimal 43 (or hexadecimal 2B) is defined to be + (plus sign).

Plus

see also