Expander can mean:

• In gas liquefaction plants, natural gas processing plants, petrochemical plants and many other industrial process plants, a turboexpander or turbo expander or expansion turbine.
• In signal processing, the opposite of a compresser, used to expand the dynamic range of a signal. See audio level compression and signal compression.
• In mathematics, "a sparse graph with high vertex or edge expansion". See expander graph.