In plain English: ERC-1400 is an older, draft set of Ethereum rules for security tokens that can block or force transfers.
ERC-1400 (draft, 2018) is an umbrella suite: ERC-1594 (transfer validation, off-chain data), ERC-1643 (documents), ERC-1644 (controller/forced transfers) and ERC-1410 (partitions) (spec). ERC-1410 defines balanceOfByPartition, transferByPartition and operator transfers, i.e. “partially fungible” balances useful for lockups and share classes (ERC-1410).
ConsenSys UniversalToken is a reference implementation with certificate-based validation (GitHub).
Sources
Public originals for the facts on this page.