Yule-tide is an archaic term for the festival of Christmas. Yule is just a shortened form of that.
A Yule-log is either a real log, or one made from cake and covered in chocolate. Guess which is my favourite! (Coincidentally, the next word in my dictionary is ‘yummy’) Traditionally a yule-log really big piece of wood, which would be set alight on Christmas Eve to signal the start of the festivities, and would hopefully keep burning until twelfth night, when the feasting and frivolity would stop.
I don’t have any kind of yule log this year, but I do have a nice big tree stump, which would probably burn well – although I think it looks better left in the garden. This is it at the end of last winter.