Rare earths is the general name of 17 elements of scandium, yttrium and lanthanide series in Group ⅢB of the periodic table of elements, and it is usually abbreviated R or RE. The luster of rare earths metals is between silver and iron. Rare earths metals have high chemical activity.

Rare earths oxides refer to 15 lanthanide series oxides with atomic numbers from 57 to 71 and scandium (Sc) and yttrium (Y) oxides in the periodic table of elements, they are 17 elements oxides with similar chemical properties.