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A BIE mint error or variety is exclusive to Lincoln Cents and is caused by a die break in the area of LIBERTY, and involves the letters BE. The die break is between the BE and looks something like an I, so it's calle B-I-E or BIE error, variety.

The die break is an actual piece of the die that fell off the die and the planchet metal filled it in, so a BIE error break will look raised and irregular.
What Is A BIE Mint Error?