Threads. What are threads in a poem?

The invisible mechanism to fasten words to a page. Or to a screen. Or is it more akin to the successive meanings in an email and/or CP (cell phone) conversation. Or the lack of meaning, thereof.


What is thready food? Celery. Of course, I've not come upon a cookbook which celebrates celery.
For that matter, doesn't seem that celery is too often highlighted in poetry. Is that your experience?