The Hebrew verb kaphar means to atone, to cover over, to make propitiation, or to ransom. It is the central sacrificial term of the Levitical system. The noun kippurim (from the same root) gives us Yom Kippur — the Day of Atonement. The word conveys the idea of sin being covered and relationship with God being restored.
Kaphar is the theological engine of Israel's entire sacrificial system. On Yom Kippur, the High Priest entered the Holy of Holies to make atonement (kaphar) for the nation's sins through blood sacrifice. The blood of bulls and goats could not ultimately remove sin (Hebrews 10:4), but the entire system pointed forward to Christ's atoning sacrifice. The New Testament interprets Jesus as both the High Priest and the atoning sacrifice — His blood makes the ultimate kaphar that the Levitical system only foreshadowed. Kaphar thus stands at the very heart of biblical soteriology.