Discussion is an extended communication (often interactive) dealing with some particular or an exchange of views on some topic.While lecture is teaching by giving a discourse on some subject (typically to a class) cowboy...

Lecture is something which a professional gives to spread knowledge like lecture in school, college etc Discussion is two way communication in which both talker and listener share their ideas. it is more informal type of communication . like Group Discussion. discussion with friends. Sometimes lecture can be a discussion if the interaction of students(or listener) is more. But a discussion can rarely be a lecture :)