For the meaning of Tanka you could look it up on Wikipedia.
OR
One Minute Writer explains it like this:
Tanka is a form of Japanese poetry thousands of years old, very similar to haiku. It's short, easy, and doesn't need to rhyme so it lends itself well to TOMW.
The 5 unrhymed lines go in syllables of 5/7/5/7/7. (So, five syllables in the first line, then seven in the second line, five in the third line, and so on.) If you're really clever with your tanka, the first three lines read together form one complete thought, and the last three lines read together form a different complete thought - but don't get overwhelmed by trying to make that work if it's too much. Just write and see what words you can come up with!
A quick brainstorm should yield several words or phrases, then just take a minute and fit them into the 5/7/5/7/7 pattern. And there you have it: Tanka! (You can definitely take more than one minute today if you need!)
Here's an example, courtesy of Craig Cornish at Poetry Soup.
Sensei
hidden in the woods
the last of winter melting
where fiddleheads grow -
it will be lonelier here
harvesting these without Dad.
So here is my Tanka with the topic Chocolate.
Chocolate for me.
It is hidden in my desk.
I really should share.
But the selfish me says, "No"
I will eat it all alone.
