The specific term for what you're describing would be
Release Management and the
Software Development Life-Cycle. You may also find the Wikipedia article on the
Software Release Life Cycle to be helpful as well.
Releases are often considered major updates to the software, but might also be brand new versions of the software. Updates are typically smaller patches that fix existing functionality or add less significant features. What each of these mean really depend on your company's specific approaches and internal lingo. For example, some companies might provide free updates containing just bug fixes but charge for releases of new features. Some companies call updates "releases" as well, as the term can be used more generically, but it can be useful to differentiate them.
Update deployment cycle depends on your company and products as well. Many companies offer a new release every year or every few months, with updates coming out every few weeks. Some companies only offer a new release every few years and offer updates quarterly. The type of product you're selling and the development methodologies you're using can significantly change your release schedule.
Roadmaps are typically internal items used by the business teams (product managers) to plan and schedule new features and fixes. Your company may choose to post a public roadmap to let customers know when you hope or expect to have new features added to your product. However, many companies avoid doing this because the roadmaps may be seen as advertised promises to customers, who could potentially sue or become upset if the features are cancelled or released late.
Milestones are often designated during project planning to help evaluate the progress of a feature or product's development. They are usually marked by the completion of a specific subtask of the project. Having milestones can provide clear goals to work towards for each phase of development, and can give you a sense of how rapidly development is progressing compared to expectations.
There are a lot of good books on the subject, and Wikipedia has a surprising amount of well-written articles on software development as well. These ideas and good implementations thereof are really more nuanced than can be summarized here.