Walling in general is a term that is used when the ranker, intentionally or not, makes the promotion requirement go higher.
Every ladder in the round has it's own Ladder Base Point Requirement or LBPR (see ladder page for more details). In order to promote to the next ladder, the first promoting ranker has to reach at least LBPR + 1 points. After the first ranker promotes out, their points_at_promotion become the new promotion_requirement for other rankers. This happens each and every time for every consecutive promotion. But what if the player never promotes or promotes after staying at top-1 position for extended period of time? Raising the promotion requirement for a significant amount is considered walling.
Active walling is the type of walling in which the waller powers up and stays at the top-1 position on a preferably empty ladder and promotes right before the player from the previous ladder would promote up.
Usually happens in longer round types and is a very effective weapon against Farmers.
Passive walling is the type of walling in which the waller powers up on a populated ladder and stays at the top-1 position awaiting for the vinegar throw. If the following ranker has autopromote active, after the successful throw at waller they promote and promotion_requirement gets raised and the waller speeds back up to reclaim the top-1 position.
Usually happens at the start of a round and in a faster round types.
Unintentional walling is considered the most harmless type of walling in which the ranker would raise the promotion requirement by being away from the game.
Usually happens in overnights when the ranker would be left on a new ladder without active autopromote. This wouldn't raise promotion_requirement too high because rankers would be left without any upgrades and therefore with a lot less power than active or passive wallers.
Also might happen in late-game top ladders due to the lack of rankers to unlock the promotion.
Waller is the ranker that deliberately powers up and stays at top-1 position for as long as possible in order to raise the promotion requirement as high as possible.
promotion_requirement go higher.vinegar_count early.