Both of them can cover a wide range of events, and there’s a big overlap in their usage. So there’s no clear cut-and-dried line between the two. The typical usage of them varies between fields, countries, and individual institutions or evengs; I’ve known things which were called a seminar at one place that would have been called lectures at another. That said, trying to set down the differences in what they’re typically used to mean:
as you say, a lecture usually means less interaction — typically one person lecturing at the front of the room, perhaps taking questions from the audience. A seminar can be like this, but can more often also involve more substantial interaction, up to general discussion.
a lecture typically has more difference in expertise between the lecturer and audience: a professor lecturing to students, a professional to a lay audience, or an expert on some topic to researchers who aren’t necessarily specialists in it. A seminar is more likely to have its presenter as a “first among equals”.
some more specific senses: a coherent series of talks presenting a single topic is usually called a lecture course; a one-off general-audience talk is usually called a public lecture; a regular series of research-level talks is more likely to be called a seminar series, or a research seminar.
Again, these are all differences in typical usage; I’ve seen most of these tendencies broken sometimes, and I’m sure that beyond my experience (mathematics and computer science, in Western Europe and North America) their usage varies more widely still. But these are a start.