202106211532 - build target host What's all this about

https://5031d9ad.nix-dev.pages.dev/tutorials/cross-compilation (via https://github.com/nix-dot-dev/nix.dev/pull/160) says build platform is were the executable is built vs. host platform where it is run. target being kind of transitive thing where you build a compiler on build and then compile code on host with that for. can be the same as host I guess. theoretically even could be the same as build although I can’t imagine how the extra host platform would make sense then.