From current wiki for low_res:
For images less than 500 pixels wide or 500 pixels tall.
I've been doing cleanup on this tag lately and it seems that there is a little confusion on it at the 500x500 resolution. The other "*_res" tags all state that the tag includes the given value, but this says less than which would be 1-499. Some tag low res at 500 pixels currently, while others stop at 499 pixels and remove the low_res from images at 500.
Should we update wiki to say "For images no more than 500 pixels..." so that it includes 500 and follows the verbiage of the other res wikis? Having it include the value would hopefully avoid the confusion as well.
Additionally, I'd like to propose updating the guideline for this tag to be "...500 pixels in both width and height."
Currently for hi_res, absurd_res, and superabsurd_res you use the appropriate tag if it meets requirements in a single direction. With the way the low_res tag is currently worded with same guideline, it is possible to have an image uploaded with res of 10000x400 which would have low_res in addition to superabsurd_res...
So, basically, I'm for updating the wiki to read:
For images no more than 500 pixels in both width and height.
Updated