Functional
To begin to understand the meaning of the phrase functionally equivalent, you must know what the words mean. Functionally is used to describe the functions of anything. A function is the way in which something is used or can be used. To be functional is to be usable. A printer's main function is to put words and images onto paper. If a printer is unable to do this, it can be described as nonfunctional.
Equivalent
Equivalent is used to describe one object's relationship to something else. It can also be used to describe one particular facet of an object instead of the whole object. Equivalent roughly means the same. A single 20-dollar bill is equivalent to 20 one-dollar bills. This is true because the monetary value of both is the same. The two groups of dollar bills are not equivalent when discussing the weight of the paper or surface area they can cover, but they can be called equivalent when the focus of discussion is narrowed to their monetary value. This is the meaning of the word equivalent.
Functionally Equivalent
When using the phrase "functionally equivalent," you are describing an object that is different from another object, but can perform the same functions. For example, a soda machine that can make change for dollar bills is functionally equivalent to a change machine that is designed to make change for dollar bills. Two functionally equivalent things don't necessarily need to be tangible. Ideas and methods can also be functionally equivalent. Two philosophical schools that see the world in different ways but come to the same conclusion could be described as functionally equivalent.
Use of Functionally Equivalent
The phrase "functionally equivalent" is used in many different fields. When discussing the translation of literature, notably the Holy Bible, functionally equivalent describes a specific method of translating the original text. This method does not literally translate the text word-for-word, but takes liberties with the exact phrasing without sacrificing the meaning. Since the words are different but the interpretation is the same, the words are functionally equivalent. The phrase is also used in computer software to describe different types of data that perform the same function, such as decimal and numeric.