$('th', $table).each(function(column), confused parameter?

$('th', $table).each(function(column), confused parameter?

I was new to jquery area, and I learning Jquery through Learning jQuery : Better Interaction Design and Web Development with Simple JavaScript Techniques.

that book has example.
$('th', $table).each(function(column) {................}

what's the $('th', $table) meaning about? it mean go through 'th', $table like ['th', $table] ?