Sharepoint Server 2010 -  the current "paid" version of Sharepoint, providing features beyond those provided in Sharepoint Foundation 2010. You're likely to need this if you're planning to use SharePoint for an enterprise-wide knowledge management system.

Sharepoint Foundation 2010 -  the current free version of Sharepoint, which provides a good deal of core functionality.  This version is can be absolutely fine for building a corporate intranet.

WSS / Windows Sharepoint Services -  the previous free SharePoint product - now replaced by SharePoint 2010 Foundation.

MOSS / Microsoft Office Sharepoint Server 2007 - the previous "paid" version of SharePoint, now replaced by SharePoint 2010 Server.

Web Application / Web App - also known as a virtual server and an web site / application pool (in iis), web apps allow for logical separation of sharepoint content. each web app runs under a different process on the iis web server.

two examples of different web apps are the central administrator site which runs on an arbitrary port number and then standard sharepoint sites which typically run on port 80. they both run under separate processes in iis.

Site Collection / Top Level Site / Parent Site / Spsite - a site collection is a web site that can contain sub-sites (aka webs), which all share the same owner and administrators of the Top Level Site Collection.

a site collection controls global settings that sub-sites underneath it inherit. settings can include permissions, storage quotas, and themes, etc...

Webs / Sub-sites / Spweb - these are web sites that live underneath a site collection. these are almost the same thing as a site collection but the difference is the global settings that are applied from the site collection.

webs can have their own independent settings separate from its parent site collection, but it makes it a bit easier to manage for the owner of the site, that's the idea here.

Lists - a list is a generic term used to define the different places to store content in a sharepoint site. some built in lists are document libraries (upload and share word docs), picture libraries (upload pics), and custom lists where you define what you want to store.