The meaning of the first three optional parameters is exactly the same as in the Allow command.
Indexer skips downloading and parsing the documents with URLs that match the given patterns.
Every time a matching document expires, indexer just marks the document as fresh again by modifying its next_index_time value. Indexer does not touch word and section information about the document. This command can be useful for excluding sites from re-indexing, e.g. when they are temporarily not available.
It's possible to use multiple patterns in the same Skip command, as well as multiple Skip commands in the same indexer.conf file.
Skip commands have global effect for the entire indexer.conf file.