I can read music or hear music and usually come up with a strum pattern on the guitar. Usually get close enough then perfect over time. However, recently I thought that I would like to get a certain song into the set listing, and when I found some sheet music online for [Tracy Chapman's "Give Me One Reason"](https://www.sheetmusicdirect.com/se/ID_No/157893/Product.aspx), it says at the top that the "strum pattern" is "6".

By looking at the music and hearing the groove, I know that it is D DU UDU, so the actual strum pattern for this song is not my question.

Where is strum pattern 6 defined? Is this defined somewhere?