In general, "aircraft-grade aluminum" can refer to any number of aluminum alloys commonly used in the construction of aircraft. It has also become popular as a marketing term for other types of products made from aluminum.
Aluminum is not suitable as a construction material for aircraft on its own, but it lends itself well to mixing with other types of metals in alloys that have suitable characteristics to protect aircraft flying at high altitudes and in low temperatures. Scandium and titanium are two elements commonly used with aluminum. These alloys are also used for some commercial products, such as softball bats and tent poles.