Mass timer buildings are prefabricated structures made of (hopefully renewable) wood. The pieces are made in a factory and then able to be quickly constructed together on-site.
This can hopefully greatly reduce the amount of carbon in the atmosphere from producing a building. The cost of producing buildings in this method is also going down. Additionally, these mass timer buildings are typically more dense than single family homes, which can lead to more sustainable communities.
I didn’t mean it in a derogatory way. Commie blocks weren’t perfect, but they were a massive success.