A fibre is a thin thread of a natural or artificial substance, especially one that is used to make cloth or rope.

A particular fibre is a type of cloth or other material that is made from or consists of threads.

Fibre consists of the parts of plants or seeds that your body cannot digest. Fibre is useful because it makes food pass quickly through your body.

A fibre is a thin piece of flesh like a thread which connects nerve cells in your body or which muscles are made of.

If you say that you feel something with every fibre of your being, you mean that you feel it very deeply.