You can use both a blog and a website to publish on the Internet. These days there doesnt remain much of a difference between a blog and a website since many web designers and developers these days are using blogging software to manage and publish websites that have got nothing to do with blogging. In order to understand the difference between a blog and a website you must know what a blog is and I safely assume that you know what a website is.
What is a blog
Blogging began with online journaling where people used blogs to publish their day-to-day thoughts and share them with family, friends and colleagues. In a blog there is mostly a first page that contains a collection of recently posted blog posts and then on the side or in the footer you have various links that you can use to jump from post to post and archive to archive. The content on a blog is mostly arranged in a linear fashion with the latest post appearing at the top. You can use a blog to chronicle your day-to-day activities, your learning process, news and updates about your organization or product, publish your literary thoughts and scientific findings and discuss all sorts of social as well as political issues. Blogging is perhaps the easiest form of publishing. You can either use one of the freely available blogging platforms to post your blog or you can register your own domain name and then publish your blog under that domain name: it all depends upon how comfortable you are setting up things.
So the basic difference between a blog and a website is that on a website your main page remains static (it is constantly changing in case of a blog) and other pages contain mostly static information. On blogs — at least on majority of blogs — you can leave comments and interact with bloggers and other visitors. Most of the times this does not happen in case of a website although even on a website you can have online forums and discussion threads.
Corporate and organizational websites follow professional, formal approach of presenting information to the visitors. Blogs are a bit informal; you can just let yourself lose and talk to your visitors informally. Some people say that you need to get a website designed whereas you dont need to get your blog designed but I dont believe in that. If you are a serious blogger then you must pay close attention to the way your blog looks and you should hire a professional web designer to get the main theme of your blog developed.
Many companies and organizations these days simultaneously manage blogs and websites. The greatest benefit of publishing a regular blog is that blogs are indexed by search engines with greater frequency compared to conventional websites because they expect the information on blogs to change very fast, and in fact the information does change on a daily basis on a blog. People dont have much incentive to visit the conventional website but they do visit company blogs regularly in order to seek new information and tips. They are also interested in taking part in the ongoing discussions on the comments section. This increases overall traffic to the blog and the main company website can bask in the glory of the blog (that is, get more traffic through the blog).
So given a choice should you have a blog or a website for your company? I would suggest you have both but you run them under a single domain. For instance you can have the main company website under your domain name and then under a subdirectory you can run your blog. This way you dont have to maintain two separate domains and the effect of traffic is greater when all the visitors are coming to a single domain.