I will attempt to explain these mystery tags which are seldomly used for their proper purpose.
Ideally you would wrap <tr> tags in a <THEAD> or <TFOOT> for long tables which would allow the browser to repeat the table headings if the table wraps to multiple pages. Unfortunatly, due to the lack of inovation in MS Internet Explorer this does not happen. It will happen in Mozilla of course. Thankfully there is a workaround in CSS for this.
<style>
thead { display: table-header-group; }
tfoot { display: table-footer-group; }
</style>
Example Page, and credit to my source of information.