Relative indexes are those where the documents are stored in or below the directory containing the indexes (e.g. \Main index\Index1), but where the full path name is not relevant.
Absolute indexes are those where the documents are stored without consideration to the placement of the index files and the index entries contain the full drive and path identification (e.g. C:\Program Files\Perceptive Enterprise Search\Main index\Index1). Publication of absolute indexes will require that the client has exactly the same disk and directory structure for the documents as you do.
When publishing indexes, it is recommended that you distribute relatively structured indexes.
If the index is completely relative, the index and documents may be distributed as long as the sub-directory structure under the index root node is preserved on the remote machine. If the index is not completely relative, you may need to use the PathToDocs statement.