The near-standard *NIX backup utility, dating way back from Version 6 AT&T UNIX. It is capable of creating incremental backups (and note which files need to be backed up), splitting the backup across multiple backup tapes, and compress data. Splitting is done based on size calculation or end-of-tape signals.
The data is, unsurprisingly, restored with command called restore.
There is, however, some opposition to it - one of the critiques presented against it is the fact that it is tied to the underlying filesystem type.
Linus Torvalds notes¹ that it doesn't work properly in Linux 2.4 and probably will be working even worse in 2.5, says anyone who uses it is "playing Russian roulette with their backups", and says it was a "stupid program in the first place". (Which leaves us with tar and feather, similar open source tools, or perharps BRU?)