"." sign is one of the "string" operators of PHP. The "dot" operator - "appends" a string from the other.
With that said, "body" ($body), variable was first set somewhere in your page, and thus, was reused again to concatenate the previous value to the one that you've pointed out. This means, that you need to find probably a file that was sorted earlier before the file to where you found this code.
Please check header.php or "index.php" of your file-structure, where the "header" is probably set.
For more info, you might find these links useful:
Hope that helps.