Webinars and Webcasts are terms that come under the umbrella term "Web Conferencing". At most times any terms like "web event," "webcast," "webinar," and "web conference" are used interchangeably. But they do have clear distinctions which become especially important in dealing with vendors who sell different types of web conferencing services. Making distinctions will help you choose a service that best suits your requirements.
As such, both terms can be encompassed under web conferencing. But the contexts with which they are used and the technology involved differ distinctly.
A webcast is a web based broadcast of something. It can be a video, an audio stream or even a power point presentation which is dispersed to a large audience through internet. That way, even the videos in YouTube can be called web casts. Other examples could be the tutorials used for online training, an important fashion show being broadcasted on the web and the like. It is a valuable and interesting tool for marketing or promoting something. Instead of making a drab written piece your promotion material, you can incorporate the same thing into a web cast and make it interesting for the audience. However it is a one-way flow of information and does not allow the audience to participate. They are merely spectators here. Their opinions and doubts cannot be expressed and does not reach the propagator.
With a webinars, things get interactive. It is a seminar aided by the web. It attempts to produce effects similar to a live seminar. In its simplest form, a seminar is streamed in the through internet. Audience participates, ask questions and give opinions. To draw more audience into participation, polls, surveys and ratings can be incorporated. Some platforms also allow live chat which is effectively contributes to the success of a webinars. Although they are mainly used for propaganda, it is very educative and connects the audience with the business in an effective way.
In understanding the difference between the two, we should be able to judge the kind of technology and equipment that may be needed for both conferencing services, which clearly is different from each other. So in dealing with a vendor who may sell a composite web conferencing package without making a distinction, knowing the difference between the two comes handy. Also, you can put them into best use for the purpose you are using it.