In order to provide more clarity - Maybe change it to:

Using 'Amazon Multipart Upload' you can upload data as a set of parts using parallel threads. This non-negative integer value (representing bytes) is used to provide the threshold after which the upload to the S3 bucket will be done using 'Amazon Multipart Upload'. Amazon recommends the size to be 100 MB. The minimum threshold for 'Amazon Multipart Upload' is 5120 bytes.

Further questions:

* What is the default value? 
* What is the max value?