The jump command is similar to a function call in a programming language. Given the label of an ancestor select or relative select command, it will immediately jump to and start executing from there. Once execution of that command is done, it will continue where it left off.
The jump command is useful when extracting data from a nested structure. For example, in a nested comment thread, the comments may be arbitrarily deep. To extract the full structure of the comments, you would define a relative select between parent and child, extract the relevant information, and then jump to the relative select to recursively extract the entire comment tree.
The label of the ancestor select command that you'd like to jump to.