Limb difference is the partial or complete absence of or malformation of limbs (arms and legs). There are two main types of limb difference: congenital limb difference and acquired limb difference.
Congenital limb difference is also referred to as "limb reduction" or "congenital amputation" or "amelia" and occurs when someone is born missing all or part of their upper and/or lower limbs.
Acquired limb differences is also known as "amputation" and occurs when someone has a limb removed for medical reasons, or accidentally due to trauma.
Definitions from: Amputation Limb Coalition and Limbs 4 Life Australia's Fact Sheets
According to the Amputee Coalitions's Limb Loss Statistics
There are nearly 2 million people living with limb loss in the United States
Among those living with limb loss, the main causes are vascular disease (54%) – including diabetes and peripheral arterial disease – trauma (45%) and cancer (less than 2%)
Approximately 185,000 amputations occur in the United States each year
African‐Americans are up to four times more likely to have an amputation than white Americans
And according to the Centers for Disease Control and Prevention's Facts About Upper and Lower Limb Reduction Defects
Limb reduction is when a part of or the entire arm (upper limb) or leg (lower limb) of a fetus fails to form completely during pregnancy. The defect is referred to as a “limb reduction” because a limb is reduced from its normal size or is missing.
CDC estimates that each year about 1,500 babies in the United States are born with upper limb reductions and about 750 are born with lower limb reductions.
In other words, each year about 4 out of every 10,000 babies will have upper limb reductions and about 2 out of every 10,000 babies will have lower limb reductions. Some of these babies will have both upper and lower limb reduction defects.