Coinblocks stored (CBS) are the net volume of coinblocks which are added to the aggregate at each blockheight. It is calculated as the difference between coinblocks created (CBC) and coinblocks destroyed (CBD).
A coinblock is the lowest level and fully fungible unit of measurement within the Cointime Economics framework. A UTXO containing 2.1 BTC (coin volume), and with 400 confirmations (lifespan) will have accumulated a cointime of: 2.1 * 400 = 840 coinblocks.
This metric was developed within the Cointime Economics framework for Bitcoin. This project was a joint venture between Glassnode and ARK Invest, with full details available in two formats: an overview primer (Version I published via ARK) and a comprehensive guide for specialists (Version II published via Glassnode).