Terms of the form are called applications. Applications model function invocation or execution: the function represented by is to be invoked, with as its argument, and the result is computed. If (sometimes called the applicand) is an abstraction, the term may be reduced: , the argument, may be substituted into the body of in place of the formal parameter of , and the result is a new lambda term which is equivalent to the old one. If a lambda term contains no subterms of the form then it cannot be reduced, and is said to be in normal form.
Terms of the form are called applications Applications model function invocation or execution the function represented by is to be invoked with as its argument and the result is computed If (sometimes called the applicand) is an abstraction the term may be reduced  the argument may be substituted into the body of in place of the formal parameter of  and the result is a new lambda term which is equivalent to the old one If a lambda term contains no subterms of the form then it cannot be reduced and is said to be in normal form