The bulk update request #15196 is pending approval.
create alias belly -> slightly_plump_stomach
Unsurprisingly (with its name being a synonym for stomach), the belly tag is being constantly yet unintentionally vandalised by users who often have no idea both tags exist, let alone how they're different. topic #21334 attempted to fix this by renaming it to plump_stomach, but was bogged down by concerns that belly is actually only for "somewhat plump stomachs" and that the new name would encourage users to tag it on characters who had more than just a slight belly (even though this had already been happening for years).
Belly needs to be renamed and deprecated ASAP. The longer we wait, the more mistags we'll have to clean up; even browsing just the first two pages I found post #6073080, post #6049313, post #6048552 and post #6046564. (I don't really care what it's renamed to; I only chose slightly_plump_stomach because of the issues people had with the previous BUR.)
Supplementary issues with belly
As a side note, since belly is only for "somewhat plump stomachs", some other issues arise. Stuff like post #6055830 and post #6037226 routinely come up when searching the tag, which could easily be someone adding it to any stomach that isn't completely flat - and with post #3092287 listed in the belly wiki as a prime example of the level of stomach required, this makes complete sense. Comparing it to that example, one could probably make the case that a good half of the stomach -belly search qualifies for belly.
Additionally, according to the wiki there's currently no tag for moderately plump stomachs. belly's wiki and examples indicate it's only for slightly plump stomachs, while big_belly's wiki states it's only for large stomachs like those found on fat and pregnant characters. As such, moderately plump stomachs are stuck in a kind of limbo, being tagged belly, big_belly or just plump on the whim of the uploader
While it's not the focus of this initial BUR, it's important to note these other shortcoming of the belly tag. It's in need of either a massive cleanup and a sister tag for moderately plump stomachs, or a wiki rewrite to expand its definition to include moderately plump stomachs.