A compactor is a machine or mechanism used to reduce the size of material such as waste material or bio mass through compaction. A trash compactor is often used by business and public places like hospitals to reduce the volume of trash they produce. A baler-wrapper compactor is often used for making compact and wrapped bales in order to improve logistics.

In geotechnical engineering, soil compaction is the process in which stress applied to a soil causes densification as air is displaced from the pores between the soil grains. When stress is applied that causes densification due to water being displaced from between the soil grains, then consolidation, not compaction, has occurred. Normally, compaction is the result of heavy machinery compressing the soil, but it can also occur due to the passage of, for example, animal feet.