A lecture is a talk on a particular subject given in order to teach people about that subject, for example by a university or college teacher.

Criticised by educators and methodologists as a one-way communication which does not involve significant audience participation, lectures have nevertheless survived in academia, mainly as a quick, cheap and efficient way of introducing large numbers of students to a particular field of study. In past centuries the diffusion of scientific knowledge via handwritten lecture notes was an essential element of academic life. Even in the twentieth century the lecture notes taken by students, or prepared by a thinker for a lecture, have sometimes achieved wide circulation (see, for example, the genesis of Ferdinand de Saussure's Cours de linguistique générale). Many professors were, and are, accustomed to actually reading out from their own notes for exactly that purpose. Today, the use of multimedia presentation software such as Microsoft PowerPoint has changed the form of lectures, bombarding the audience (as critics such as Edward Tufte put it) with unnecessary and possibly distracting or confusing graphics.

Other forms of academic teaching include seminars, workshops, and tutorials, while in schools the prevalent mode of student-teacher interaction is lessons. Many university courses relying on lectures supplement them with smaller discussion sections or laboratory experiment sessions as a means of further actively involving students. Often these supplemental sections are led by graduate students rather than senior faculty.

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"Lectures," said McCrimmon, "are our most flexible art form. Any idea, however slight, can be expanded to fill fifty-five minutes; any idea, however great, can be condensed to that time. And if no ideas are available, there can always be discussion. Discussion is the vacuum that fills a vacuum. If no one comes to your lectures or seminars, you can have a workshop and get colleagues involved. They have to come, and your reputation as an adequately popular teacher is saved." (John Kenneth Galbraith, A Tenured Professor)