At the moment, the gaping tag wiki states that it should be used for
An anus or pussy that stays open by itself, typically after sexual intercourse.
Be careful not to confuse this with invisible penis + a spread pussy or anus, which has the same visual effect of the orifice being spread open for no apparent reason. However, that occurs during sex, whereas this tag is for afterwards.
As far as i know, the practice of spreading the inside of an orifice through the use of fingers/tentacles/whatever is called "gaping" (post #4254995, post #4373495 are the only examples i can find at the moment). However, as of now there's not really a way to find it easily.
Gaping requires the orifice to stay open by themselves, and spread_pussy/anus is almost exclusively used for the spread of the outer lips/asscheeks.
I'd suggest converting gaping to something like unassisted gaping, but it may be too rough a change since the tag is quite old.