A build is an actual compilation of the code into executable file(s) which is then ran/tested in some way. You can have many many builds for each version.
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Generally, the Version is the goal that contains the overall list of features and bug fixes that will released that is usually defined by the Product/Marketing folks. In software development, the team will divide the features and bug fixes into manageable portions. Developers work on a set of portions and product a Build. That Build is then tested and evaluated for the set of items that where worked on. And repeat.
When it is determined that enough features and bug fixes have been complete and all the testing is consider complete, it is released to the "Public". With all those values, it allows the development team to go back and recreate a specific build from the source code to make fixes.