This colloquial phrase is used to describe someone who is extremely thin. The '80 thread' refers to the thinness of a thread that is 80 denier, a unit of measure for the linear mass density of fibers.
Examples
- Spanish: ¡Madre mía, has perdido mucho peso, estás como el hilo 80!
- English: My goodness, you've lost a lot of weight, you're as thin as a rail!