I gather this has a meaning related to "version". However, I have seen this term used for military and commercial aircraft and other products (generally connected to government or aerospace).
I am looking for a formal definition of the term (not opinion) as used in these industries. How is it different from "version"? What's makes a change to a design a "version" rather than a "block"? What's an "update" vs. a "block update"?
EDIT: I did see this answer prior to posting my question:
The difference is that what is marked as an answer there is really mostly opinion. What I am looking for here is an industry definition of the term rather than opinion. In other words, if you used the term "block" in a contract, what would it mean?
It is clear that colloquially it means "version". Yet they don't use the term "version" at all. They don't say "Falcon 9 Version 5" or "AC-130 version 10", they explicitly use the term "block".
There might be no formal definition distinct from "version". This might be a term of trade that could equate to, for example, the use of "basis points" in financial speak instead of percentage. Yes, a basis point is 0.01% and it might be more convenient in financial speak, but saying "75 basis points" and "0.75%" is the same thing (and the latter requires no mental gymnastics). Same thing with the term "thou" in machining, which means "0.001 in".
I think in both of the examples I gave there's a pretty straight forward equivalence or definition of the terms ("basis point" and "thou"). I have not been able to find such a definition for "block". Does block mean "major version"? In other words, you have "Falcon 9 block 4 version 4.99" and when you make the jump to what would be version 5.0 the language becomes "Falcon 9 block 5"?
The examples given are not meant to be perfect. No need to nit-pick them. Just trying to clarify a perspective.
EDIT 2: I also read this question and answer. Once again, no definition is provided, just opinion: Why is the word 'Block' used along with a number to indicate the rocket version?
I think a definition would require a link to a NASA (or other authoritative source) standards or nomenclature document defining how the term is to be used in programs.
What made this confusing for me is that I am working on a project where the statement of work says something like (sorry, can't quote exactly due to restrictions) "allowance for version and also block upgrades". Yes, I will ask the author but wanted to see if there's a canonical definition of the term in the space industry. A search did not return anything I can use.