Building Blocks are one of the oldest toys extant - dating from the late 1700's at least. But it's not a surprise to discover that modern parents reared on plastic and screens are unfamilar with what can be done with them. The "Building Blocks" metaphor is ubiquitous, it's still used everywhere to mean "modularity." But this is a toy for children as old as 13 - Legos only 70 times as big. When people talk about "building blocks," they are talking about something that is an amazingly versatile and durable toy recommended by teachers worldwide.
Here they are: Building Blocks.