Hogmanay is the Scots name for New Year's Eve.
It is much, much more important to the Scots than Christmas, which is seen as a purely religious/children's day - although it has become much more Anglicised nowadays and seems to be going more towards the English style Christmas, with too much commercialism for my tastes!
Preparations start weeks before Hogmanay. Houses are given a 'deep clean' and rooms are re-decorated in time to greet the new year!
Any arguments or family rifts are expected to 'try' to be healed.
Edinburgh hosts what it calls the biggest street party in the world - here's the website.
There are lots of traditions, like First Footing people, waiting to hear 'the Bells' which signal new year..... eating and drinking far too much, with traditional dishes like Steak pie, Black Bun, shortbread etc...
Here's a bit more info