I have always thought of Blocks in Solana (and in any blockchain really) as containing a list of transactions.
But in Solana, it seems there is also the concept of an Entry, which from what I am reading is also a grouping of transactions.
So what exactly is the relationship between a block and an entry?
A block is made of a list of entries, which are either ticks or a set of transactions. Currently, the definition of a transaction entry is: "A set of transactions that may be executed in parallel." https://solana.com/docs/terminology#transactions-entry
This definition will change with SIMD-083, which relaxes the requirement that transactions must be executable in parallel: https://github.com/solana-foundation/solana-improvement-documents/pull/83
