1. A software source tree packaged for distribution; but see kit. Since about 1996 unqualified use of this term often implies ‘Linux distribution’. The short form distro is often used for this sense.
2. A vague term encompassing mailing lists and Usenet newsgroups (but not BBS fora); any topic-oriented message channel with multiple recipients.
3. An information-space domain (usually loosely correlated with geography) to which propagation of a Usenet message is restricted; a much-underutilized feature.