Enantiomers are molecules that have  opposite spatial configuration and are known to have optical activity (mirror images).

One enantiomer will rotate polarized light a set number of degrees to the right. This is called the dextrorotatory isomer or (+) isomer, also known as "R " isomers from latin root  dexter, "right-handed", or rectus, "right, correct, upright".

The other enantiomer will rotate the plane polarized light the same number of set degrees in the opposite left direction. This isomer is said to be a levorotatory isomer or (-) isomer; also known as "S" isomer from latin root, sinister, "left"].