Oxbow code

In computer programming, oxbow code refers to fragments of program code that were once needed but which are now never used. Such code is typically formed when a program is modified, either when an item is superceded with a newer version but the old version is not removed, or when an item is removed or replaced, but the item's supporting code is not removed.

Similarly, variables and data structures can be left around after the last code that used them has gone, though these are more commonly called unused variables or unreferenced variables.

The term oxbow is taken by analogy with oxbow lakes, which form in nature when a river meanders by eroding its margins and depositing the residue on other banks, becoming ever more contorted until the water breaks through from upstream to downstream, "short-circuiting" one loop of the river. Further deposits cut the old loop off from the main flow, leaving behind a horseshoe-shaped lake with its points toward the river.

Such code is normally removed as a sanity check that a superceded item is indeed not being used any more.