1. A file created by the Tar utility, containing one or more other archived and, optionally, compressed files. From I-gloss

2. A file created with the "tar" command containing a collection of other files. From Linux Guide @FirstLinux

3. n. [very common; prob. based on the "tar baby" in the Uncle Remus folk tales] An archive, created with the Unix tar(1) utility, containing myriad related files. "Here, I'll just ftp you a tarball of the whole project." Tarballs have been the standard way to ship around source-code distributions since the mid-1980s; in retrospect it seems odd that this term did not enter common usage until the late 1990s. From Jargon Dictionary