<p>Each house has one each term, and you can’t possibly miss it since it’ll be announced, emailed, etc. etc. It’s not technically “formal” (since formal implies tuxedo for men–living in the UK for any length of time will make you very sensitive to these differences) but people dress up for it.</p>
<p>Here’s a photo from way back in my freshman year showing 3 different perfectly acceptable “takes” on what to wear to formal dinner:</p>
<p><a href=“http://lloyd.caltech.edu/gallery/view_photo.php?set_albumName=album44&id=Joe_John_John[/url]”>http://lloyd.caltech.edu/gallery/view_photo.php?set_albumName=album44&id=Joe_John_John</a></p>