uname

Print system information, print information about the machine and operating system it is run on. If no options are given, `uname' acts as if the `-s' option were given.

Syntax
      uname [options]...

Options

 -a
 --all
     Print all of the below information.

 -m
 --machine
     Print the machine (hardware) type.

 -n
 --nodename
     Print the machine's network node hostname.

 -p
 --processor
     Print the machine's processor type

 -r
 --kernel-release
     Print the kernel release 

 -s
 --kernel-name
     Print the kernel name

 -v
 --kernel-version
     Print the kernel version

 -i
 --hardware-platform
     Print the hardware platform or "unknown"

 -o
 --operating-system
     Print the operating system 

If multiple options or `-a' are given, the selected information is printed in this order:

SYSNAME NODENAME RELEASE OSVERSION MACHINE

The full documentation for uname is maintained as a Texinfo manual. If the info and uname programs are properly installed at your site, the command:
info coreutils aquname invocationaq should give you access to the complete manual.

The OSVERSION, at least, might be multiple words.
For example:
$uname -a
=> Linux hayley 1.0.4 #3 Thu May 12 18:06:34 1994 i486

“What's in a name? That which we call a rose by any other name would smell as sweet” ~ William Shakespeare

Related:

env - Display, set, or remove environment variables
groups - Print group names a user is in
hostname - Print or set system name
id - Print user and group id's
logname - Print current login name
ps - list processes
tty - Print filename of terminal on stdin
users - Print login names of users currently logged in
who - Print who is currently logged in
whoami - Print the current user id and name (`id -un')
Equivalent Windows command: ECHO %USERNAME%