what is {version} in ScriptBundle("~/scripts/jquery-{version}.js")

It allows you to indicate a version number format (semver) that many libraries use. For example, you reference jquery-1.9.1 and then it goes to jquery-1.9.2. Using {version} you don't have to change your code, you just need to re build the bundle.

See the answers to this question.

Also, check out this link. The Bundling and Optimization section discusses the use of the {version} tag.