What is adware?

Adware is a type of software that is downloaded to your computer to show you advertisements. These advertisements may take many forms, from relatively noninvasive banners within a program, to very invasive pop-up windows that come up regardless of that you are doing in the foreground.
Adware is a form of malware (any code that affects the functionalist of your system, performance, executes unwanted or unauthorized commands) that exposes a PC user to bogus and illegitimate pop ups and advertises based on the user's web habits. Adware is a threat because it is the start of more malicious crimes like identikit theft. Your probably wondering how are pop ups dangerous. Well some pop ups lend users to phishing sites. A phishing site is a sight that tricks web user into to divulging personal information. See pop ups are dangerous and the best way to avoid pop ups and dangerous downloads and websites (URL's) is to download software with all around protection. Protection that includes a firewall and pop blocker and a phishing filter.    
There are programs that download commercial banners, ad's porn sites etc. to your computer and keep showing them to you, even if you don't want them.
Answer .
Generically, adware (spelled all lower case) is any software application in which advertising banners are displayed while the program is running. The authors of these applications include additional code that delivers the ads, which can be viewed through pop-up windows or through a bar that appears on a computer screen. The justification for adware is that it helps recover programming development cost and helps to hold down the cost for the user.
Adware has been criticized because it usually includes code that tracks a user's personal information and passes it on to third parties, without the user's authorization or knowledge. This practice has been dubbed spywareand has prompted an outcry from computer security and privacy advocates, including the Electronic Privacy Information Center.
Answer:
You might think that there is only one way to look at Adware. It must be bad because there are Adware detection and removal programs right? The reality is not so simple. Adware is usually bundled with freeware or shareware programs downloaded off the internet. Did you consider the reason that program was free when you downloaded it? It turns out that there are two ways to look at Adware and you should consider both before you either slam or praise it