In organic chemistry, alpha-elimination refers to reactions of this type:
:RCHX  →  RC:  +  HX
The reaction is employed to generate carbenes and nitrenes. The formation of dichlorocarbene from chloroform is an example.
Alpha eliminations contrasts with beta eliminations, which are commonly used to generate alkenes:
:RCHCXR  →  RC=CR  +  HX
Both alpha- and beta-eliminations typically require strong base.