Maginei Eretz was the first edition of the Orach Chaim section of the Shulchan Aruch published with the commentaries Magen David and Magen Avraham on either side of the main text. This format has been maintained and today is the standard format for the Shulchan Aruch Orach Chaim.
The name "Maginei Eretz" translates as "shields of the earth," a quote from Psalms 47:10 ("... for the shields of the earth belong to God: He is greatly exalted.")
The Magen David was written by Rabbi David HaLevi Segal, and has since been referred to as the "Taz" (The abbreviation for Turei Zahav), for consistency with Segal's commentary on the Yoreh Deah section of the Shulchan Aruch.
The Magen Avraham was written by Rabbi Avraham Gombiner. The Maginei Eretz was published by his son, Chaim, following his father's death.