Chunk
A chunk is a set of elements comprising a subset of an import- or export document. A chunk's number of items is determined by the Fetch size.
A chunk can be:
a number of XML elements in case of a single document
a number of files in case of a single document and a fetch file worker
* 
If a definition contains two documents and the fetch size is set to 100, it will process chunks of 100 elements until the first document is done and will then move on to process the elements of the second document until it is done too.