What does “Liquid error: undefined method” mean?

It means a template is calling a property or filter on an object that is nil, for example undefined method ‘price’ for nil when a product, variant, or metafield no longer exists. The usual causes are a removed object, a renamed metafield, or a {{ ... }} that runs before the data is loaded. We trace the exact line, then guard the value with a default filter or an {% if %} check so the page renders cleanly instead of throwing.