processing appears to be a virtually meaningless, undefined tag attached to 112 questions. It does not appear to add any value because everything requires processing so the tag does not differentiate anything. Recommend simply deleting it (or attaching it to 240,000 other questions for consistency).
processing is used in two ways - firstly as a meta-tag. Secondly to do with the processing language/IDE.
I'd propose killing off the processing tag and merging it with a tag that specifically denotes the language - either processing-ide looks good to me, since it its a language issue, it dosen't belong here.
Amusingly, I said the very same thing as a question some time in the past.