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%USERPROFILE%

The directory pointed at with the environment variable %userprofile% stores personal data of a specific user.
This value is alse found in the registry in the value of ProfileImagePath under the registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList\S-1-5-SID.
The value of %userprofile% usually is c:\Users\username (username being lowercase of %username%?)
Apparently, in Windows 10, the variable %CSIDL_PROFILE% is equivalently used for %USERPROFILE%.

Default sudirectories

Predefined (or pre-installed) sub directories are
Name German name Junction to
3D Objects 3D
AppData
Application Data Anwendungsdaten %UserName%\AppData\Roaming% (aka %AppData%)
Contacts
Cookies Cookies %LOCALAPPDATA%\Microsoft\Windows\INetCookies
Desktop
Documents Dokumente/Documents?
Downloads Download
Favorites Favoriten
Links Links
Local Settings Lokale Einstellungen %LOCALAPPDATA%
MicrosoftEdgeBackups MicrosoftEdgeBackups
Music Musik
My Documents Eigene Dateien Documents
NetHood Netzwerkumgebung %APPDATA%\Microsoft\Windows\Network Shortcuts
OneDrive OneDrive
PrintHood Druckumgebung %APPDATA%\Microsoft\Windows\Printer Shortcuts
Recent Recent %APPDATA%\Microsoft\Windows\Recent
Saved Games ?
Searches Suchen
SendTo SendTo %APPDATA%\Microsoft\Windows\SendTo
Start Menu Startmenü %APPDATA%\Microsoft\Windows\Start Menu
Templates Vorlagen %APPDATA%\Microsoft\Windows\Templates
Videos Videos
The junctions' (aka reparse points) name and target can be shown in cmd.exe with dir /al.
%USERPROFILE% also stores the registry hive for the current user (HKEY_CURRENT_USER) in the file %USERPROFILE%\NTUSER.DAT.

Tilde and $home in Powershell

In PowerShell, the home directory of a user is stored in the automatic variable $home.
PowerShell allows to abbreviate $env:USERPROFILE or $home with the tilde (~): 
PS C:\> ls $env:USERPROFILE
PS C:\> ls $home
PS C:\> ls ~
PS C:\> cd ~
PS C:\> cd ~/Documents
Thus, the tilde seems to mimic the function it also has in bash.

Getting the user profile's path in PowerShell

A possible way to determine the path of a user's profile in PowerShell is like so: 
PS C:\> [System.Environment]::GetFolderPath([System.Environment+SpecialFolder]::UserProfile)
C:\Users\Rene

See also

%userprofile%\AppData stores application data.
The cdhom.bat script takes one to this directory in cmd.exe.
%SystemDrive%\Users
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders
The combination of the environment variables HOMEDRIVE and HOMEPATH.
The .NET enumeration System.Environment+SpecialFolder.
The equivalent of a home directory in Linux is /home/<username>.

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