I am trying to understand what is TID and how it works. I found 2 definitions of TID in the documentation:
A final identifier type used by the system is tid, or tuple identifier (row identifier). This is the data type of the system column ctid. A tuple ID is a pair (block number, tuple index within block) that identifies the physical location of the row within its table.
In fact, every pointer to an item (ItemPointer, also known as CTID) created by PostgreSQL consists of a page number and the index of an item identifier.
I understand the second definition and it's clear for me, but I struggle with the first definition and the terms it uses.
What are block and tuple index within block? How do they match with pages and the second definition?
Please help and clarify, which definition is correct and how should I understand the terms from the first definition.