The Collaborative International Dictionary of English v.0.48:

object file \ob"ject file\, object program \ob"ject program\, n.
   (Computers)
   A computer program which has been translated into machine
   language by a compiler and assembler, but not yet linked into
   an executable program; sometimes called an obj file,
   because its file name typically has the extension "obj" .
   [PJC]