Source : Free On-Line Dictionary of Computing

beta abstraction
     
        [{lambda-calculus}] The conversion of an expression to an
        {application} of a {lambda abstraction} to an argument
        expression.  Some subterm of the original expression becomes
        the argument of the abstraction and the rest becomes its
        body. E.g.
     
        	4+1 --> (\ x . x+1) 4
     
        The opposite of beta abstraction is {beta reduction}.  These
        are the two kinds of {beta conversion}.