What is ActiveX ?

ActiveX are programming modules that in terms of web design, can give dangerous functionality to client-side scripting.

Allowing unsigned ActiveX is risky (allowing it at all in IE is). Some of it is very useful, even necessary, some is dangerous and relatively pointless.

I'm assuming you're referring to Internet Explorer, in which case I suggest you use a different, more secure browser, such as K-Meleon, Opera, Netscape, or Firefox.

ActiveX is Microsoft technology used for developing reusable object oriented software components. ActiveX is an alternative name for OLE automation (OLE - Object Linking and Embedding), not a separate technology. While the term "Automation" refers to the overall technology, "ActiveX" refers to the objects that can be created and manipulated using AutomationAn ActiveX control is similar to a Java applet. Unlike Java applets, however, ActiveX controls have full access to the Windows operating system. This gives them much more power than Java applets, but with this power comes a certain risk that the ActiveX control may damage software or data on your machine. To control this risk, Microsoft developed a registration system so that browsers can identify and authenticate an ActiveX control before downloading it. Another difference between Java applets and ActiveX controls is that Java applets can be written to run on all platforms, whereas ActiveX controls are limited to Windows environments. Yes it is safe to allow your computer to install it.

ActiveX is Microsoft technology used for developing reusable object oriented software components. ActiveX is an alternative name for OLE automation (OLE - Object Linking and Embedding), not a separate technology.[citation needed] While the term "Automation" refers to the overall technology, "ActiveX" refers to the objects that can be created and manipulated using Automation.

Due to Internet Explorer and Visual Basic's popularity in the late 1990s, many people incorrectly assume that all of ActiveX is related to ActiveX controls. An ActiveX control is a special type of ActiveX object that is designed to be used similar to a plugin.[citation needed] The most common use of ActiveX controls is to build plugins for Internet Explorer.

Its a file with an .ocx extension. They are Microsofts implementation of applets in terms of IE.

More specifically, they are 'add-ons', or small additions to enhance the functionality of Internet Explorer.

More generally, they are any components that can be added to applications without much more than a reference. No additional coding needed. Makes applications extensible.

EDIT:

Safety wise, they are ok as long as you know where the ActiveX is coming from. They are considered 'unsafe' because they can be written by anyone with a computer and coding knowledge. As long as you only install those you know who they are, you will be fine.

Think of ActiveX as small computer programs you download from the internet. You dont just download WHATEVER. Put some analysis into what you are downloading and how it will be used.

It depends. Active X is a object that allows your browser to do certain thing. An example is Shockwave. What is the exact active x are you referring to? There are many types such as ones for viewing special documents or even pictures. Most are safe ti install, and if you don't want it anymore, you can delete it.