This topic is dedicated to the disambiguation and standardisation of the various tags that describe lifting legs and feet. But first, some perspective on why this is needed.
"One leg lifted up and away from the other leg so that they are spread wide apart: one in the air, the other resting."
The leg_lift wiki currently describes the kind of poses seen in post #3118262 and post #2854945. However, its non-intuitive/ambiguous name has led to it being used in place of legs_up, leg_up, knees_up, knee_up and feet_up, just to name a few.
While researching this, I discovered that all of these legs/feet tags with the "_up" suffix are as commonly misused as the others, with the only wiki standardisation being between legs_up and leg_up (and even that isn't 100%). I propose concretely defining and standardising all of these tags, and at the very least tag gardening the most recent posts featuring them so users who don't use wikis see the recent examples as correct rather than a mix of correct/incorrect.
legs_up
leg_up
leg_lift
knees_up
knee_up
feet_up
foot_up
heel_up
toes_up
For formalities' sake I'm mentioning top-down_bottom-up too but I think we can all agree that there is almost nothing that a user could confuse this with, except maybe a shirt_pull + skirt_lift combo - and even then a single cursory search should be enough to show what the tag is really for.
This big a project will require a large effort, but it's best if we grab it by the horns now rather than let it fester even longer until it's twice as awful a few years down the track. Your thoughts, input and suggestions are all very welcome, as is any effort you decide to put into tag gardening once everything is ready to start moving.
Gelbooru rulez!!!