An abrasive liquid contains substances, often minerals or inorganic substances, that are harder than the material they rub against. This abrasion will wear out and damage softer materials.
Naturally occurring abrasives found in wastewater could be sand, stones, calcium carbonate or ferric oxide.
Abrasive liquids can accelerate corrosion of a pump and is directly involved in erosion-corrosion. In general more force will cause faster abrasion. This makes high velocity parts of a pump more susceptible to erosion-corrosion.