A low stool used to support one’s feet.
Part of King Solomon’s large amount of gold was used to make a footstool for his ivory throne (2 Chronicles 9:18). The word is often used as a symbol. Both the ark of the covenant and the temple are referred to as "God’s footstool" (1 Chronicles 28:2; Psalms 99:5; 132:7; Lamentations 2:1; compare Isaiah 60:13). These were special places where God's presence lived and where he showed his power as king. Just as a king might rest his feet on a footstool while sitting on his throne, these holy places were seen as places where God's glory was present.
The Bible says that God would make the enemies of the Messiah (God's chosen one) become like a footstool under his feet (Psalms 110:1). This means God would give the Messiah complete power over his enemies, just as someone has control over what is under their feet. Many passages in the New Testament repeat this idea that the Messiah would defeat his enemies (Matthew 22:44; Mark 12:36; Luke 20:43; Acts 2:35; Hebrews 1:13; 10:13). In these verses, "footstool" literally means "something under the foot."