While there are many similarities in the way meetings and webinars are conducted, they are meant to achieve different purposes.
Online meetings
An online meeting is for conducting discussions and collaborating over the web using audio, video, and screen sharing. It is organized by a host, and attended by participants who are invited by the host. Everyone in a meeting can listen to and speak with each other, unlike a webinar.
Webinars
A webinar (or "web seminar") is an informative session broadcast over the web to educate individuals interested to learn about a particular subject. A webinar organizer sets up a webinar and promotes it among their target audience through emails, social media, websites, and blogs. Interested individuals can register for the webinar and attend it at the scheduled time.
During a webinar, the organizer delivers a presentation to the audience. The attendees remain in listen-only mode. They can type and ask questions to the organizer using the Q&A option in the webinar window. While the participants of a meeting actively communicate with each other, attendees of a webinar do not communicate among themselves at all.