1. In UNIX, the $IFS variable separates commands. It is usually conigured to be the semicolon (;) and newline characters. However, it can be reconfigured to be other characters as well. Data-driven attacks will sometimes seek to reset the IFS variable (e.g. IFS=x), then cause execution within the data field wihtout having to insert shell metacharacters. Tidbit: On Linux, the $FF variable may also be used like $IFS. From Hacking-Lexicon

2. The Internal Field Separator that is used for word splitting after expansion and to split lines into words with the read builtin command. The default value is ``<space><tab><newline>''. From Rute-Users-Guide