r/LanguageTechnology - Meaning of the word GOLD in LISA paper

It's usually short for "gold standard", as in the highest level of achievement one measures against to see how good they are. As u/useful said, they are usually data sets/labeled data hand-made by humans with expertise in the field in question. So gold (standard) syntax trees are those curated and labeled by linguists. I haven't read this paper, but I can only assume they mean that training on hand-labeled syntax trees dramatically improves the results of their system over the common practice of letting the system come up with its own labels.