Fibro is an abbreviation for "fibrous cement" - or "fibrous asbestos cement" and is a building material made of compressed fibres cemented into rigid sheets. Manufactured and sold until the mid-1980s "Fibro" in all its forms was a very popular building material.
The fibres involved were almost always asbestos based. The use of "Fibro" has since been banned in Australia due to its asbestos content.