It seems like everybody is mixing up things here. Block Trade (re: links that xandman shared) has nothing to do with the order book. There are trades that are done outside the exchange, usually with institutions, which meet a minimum volume. Once done, they need to be reported to the exchange, and usually (depending of the trading product type) they are identified in the market data feed with a special marker. As for the term 'order block', I've never heard of it.
thank you for clarifying; order block was used in original post but I assume it is block order or block trade, yes?
It's a new term for me. There's some stuff connected with forex https://www.forex.academy/learning-to-trade-the-order-block-forex-strategy/ but maybe this is more of what it's referring to; https://library.tradingtechnologies.com/adl/tb-order-block.html
On my exchanges, block trades happen off book through the block trade facility. So they don't affect the book liquidity and have zero impact on the advertised liquidity. They do show through on the tape though. It creates a real mess using order flow at rollover. My exchange experience is limited to Hong Kong Exchange and Japan Exchange Group.