V8/usr/src/cmd/Mail/manual/cmds/alias

.ip \fBalias\fP
Define a name to stand for a set of other names.
This is used when you want to send messages to a certain
group of people and want to avoid retyping their names.
For example
.(l
alias project john sue willie kathryn
.)l
creates an alias
.i project
which expands to the for people John, Sue, Willie, and Kathryn.