A permission- and subscription-based means of regular communication with current and future customers, usually distributed monthly or weekly. Available electronically, via text-based or HTML pages, they can include complete articles, or brief descriptions with links to articles on your website.
Don't spam your enewsletter - get permission and offer opt-out links Can be a good vehicle for promoting other content: webinars, ebooks, white papers, live events, etc. Can be co-branded to gain third-party credibility