HEITE and KENNING
The Old Norse skalds had two somewhat special tools when writing poetry, the heite and the kenning. Anyone who's studying Old Norse mythology will sooner or later run into these expressions and therefore an explanation may be in order.
Heite
A heite is more or less just another name for a person, place or thing. For example some heiten for Odin are Allfader, Ygg and Gangrad. For Frey some heiten are Ing, Yngve and Frö. Rather straight forward, but a heite can still be something of a code.
Kenning
Here's were the fun starts. A kenning is a metaphoric name for something, or an allegory, and sometimes you really need to know your myths to decode them. I'll use Odin as an example again. One kenning for Odin is The One Eyed God, since he has only got one eye. A more difficult kenning is the name of the world tree Yggdrasil, while it looks like a name or heite it is actually a kenning. Ygg as mentioned above is a heite for Odin, drasil means horse. So Odin's Horse, but to understand this you have to know about the myth where Odin hung in a tree for nine days, "riding" the tree. That's how kennings work.
A few more. Swords can be called "sarlaukR", meaning wound onion. Why? Well, old bronze age sword had a onion shaped blade (not like a modern round onion, but more like a spring onion), while this shape where no longer in use during the Viking era, the kenning was still alive.
Golden arm rings could be called "gift of kings" since it was customary for kings to give golden rings as gifts to warriors and skalds.
My belief is that both heite and kenning were tools that also helped the skalds to memorise and recite the myths, plus making the audience part of the story telling since to understand it all they had to have a certain amount of knowledge and even perhaps to think a bit. Probably a very clever kenning would give the skald high praise.