Actually this was the first question I was asked when I started learning SharePoint. But I can’t get clear answer for this question on that time. Spending some time with Google, I got some links and here the summary of those big article points.

WSS

• WSS is included as a part of Windows Server, specifically with Windows Server 2003, and 2008
• WSS does not have its own licensing model, Instead the use of WSS is controlled through Windows Server 2003 or 2008 licenses.

MOSS

• MOSS is a value-added set of components and services that has been build on top of WSS (Subset of WSS). In other words, MOSS takes the foundation laid by WSS and expands upon it.
• MOSS has its own licensing model that includes server-side licenses and client access licenses (CALs). The MOSS licensing model is further broken out into a Standard Edition and an Enterprise Edition. MOSS 2007, is the nexus of Microsoft Office System, It delivers the robust, enterprise-targeted features of SharePoint Products and Technologies, which accelerate business processes across the Intranet, Extranet and Internet.

The followings are the features that both MOSS and WSS provides

• Issue Tracking
• Real-time presence and communication
• Standard site template
• Wikis & Blogs
• People and Groups lists
• Calendars
• Email integration
• Task coordination
• Surveys
• Document collaboration
• Support for ASP.NET 2.0
• RSS feeds
• Recycle bin

The following is the list of things that MOSS provides that WSS v3.0 does not.

• Social Networking
• My Site
• Site Directory
• User Profiles
• Site Manager
• Portal or Enterprise templates
• Search
• Knowledge Network / People Search
• Business Data Catalog / Business Data Search
• Document Workflow
• Excel Services
• Key performance indicators
• LDAP pluggable authentication provider
• Single Sign-On (SSO)

WSS – Windows SharePoint Services
MOSS – Microsoft Office SharePoint Server

If you have SharePoint, by definition you have WSS.