Do you know what a 'portmanteau' is? It is a new word formed by the combination of two or more words. Few examples are: Bluetooth, Blackboard, TeamViewer, Skype, etc.
Here, 'webinar' is even a similar word. It is a recently coined word that is a combination of the words 'web' and 'seminar'.
It is a seminar, lecture, or a paper presentation that takes place through the Internet or what can be called as 'web'.
It is a two-way process that has an advantage of discussion and scope for improvement as well as building of healthy relationship between the presenter and the audience.
Hope this explanation helped you!
Short for Web-based seminar, a presentation, lecture, workshop or seminar that is transmitted over the Web.
A key feature of a Webinar is its interactive elements -- the ability to give, receive and discuss information. Contrast with Webcast, in which the data transmission is one way and does not allow interaction between the presenter and the audience.