Device
In HomeSeer, devices are objects that hold information.  Often these objects are tied to a real, physical device in your home so that the information it holds is the status of that real device.  A device can also hold information such as a weather forecast or the winning lottery numbers that were downloaded from the Internet.

Event
In HomeSeer, an event is a grouping of two things - actions and a trigger.  The trigger is what causes the event to be run, which is when the actions defined in it are carried out.  Actions are the commands that you want carried out when the event runs such as turning on a light, sending an infrared signal, or downloading the latest weather forecast by running a script.

HTTP
This stands for HyperText Transfer Protocol and is the network technology that transmits web browser display language (HTML) to your web browser from a server.  HTML is HyperText Markup Language.

Plug-In
In HomeSeer, a Plug-In is a program that works with HomeSeer to add some functionality or perform specific tasks that HomeSeer does not do.  A plug-in lacks much of the user interface that a standalone program would need as it uses the UI built into HomeSeer instead.  A plug-in can add triggers, conditions, and actions to HomeSeer for the end user.

Port
When referred to in networking terms, the port refers to a virtual location on your computer's network interface where a server is running, ready to respond to requests that come to it.  For example, you can have 4 different web sites hosted on your one computer just by having each one use a different port number.  By default, when you browse to a website, you are connecting to port 80 on the server, but the browser does not show you this.  When you specify a different port, you append a colon and the port number to the end of the URL like this example that specifies port 83 -- http://mycomputer.com:83

Powerline Carrier
A type of communication system that uses the electrical lines (powerline) in your home as the physical transmission method for the information signal.  X-10 is a type of powerline carrier system.

Set On/Off
In HomeSeer, there are triggers or conditions that use the settings ON/OFF/Set ON and Set Off.  A device that is ON and receives an ON signal will not trigger an event configured to check for a device that is ON because it was already ON.  The Set On and Set Off triggers allow an event to trigger (or a condition to run) if a device receives an ON command, even if it was already on.

Virtual
Anything that is virtual is everything but real.  A virtual drive on a computer for example will store data just like a physical hard drive, but it does not physically exist.  A virtual device in HomeSeer can be turned on/off or store information like the physical device it often represents, but it has no physical form.

Web Interface
There are two interfaces for controlling/operating HomeSeer.  One is the Windows interface which is what you see when you start HomeSeer on the computer it is running on.  The Web Interface is the screens you see when you access HomeSeer using a web browser after starting the HomeSeer Web Server.  You can view/add/change devices and events through the web interface.

X-10
X-10 is a form of powerline carrier technology that has been around for close to 30 years.  Coming after experiment 9, experiment 10's objective was to see if a device could be controlled remotely by sending a signal over the powerline.  X-10 was developed by Pico Engineering in Scotland and is most often associated with the company that bears the technology's name which produces devices that use the X-10 protocol.

X10
See X-10

Z-Wave
Invented by Zensys in Denmark, Z-Wave is a wireless technology completely encompassed within an electronic chip, which can be embedded within devices to give them wireless control capabilities.  Z-Wave is a relatively low-bandwidth two-way wireless network protocol.  Z-Wave devices by different manufacturers are to many degrees interoperable because the underlying technology is provided by the same electronics.

ZWave
See Z-Wave