permissionless distributed consensus protocols

Is that a block chain thing?

I think the core concept is that the entire history of a unit is encoded in the unit itself, and goes with it. Anyone can access it (permissionless), but it can't be hacked because everyone who's ever touched it has a record of its history (distributed consensus).

Then again, I may be talking out of the wrong orifice.
I think it starts to make sense if you break it down by word.

Permissionless - anyone can access it (e.g. a database).
Distributed - the details within the database/blockchain aren't isolated to specific places, like being held on a single mainframe, but distributed across the network of users.
Consensus - changes or operations within the database are effectively agreed by consensus. So, for example, if someone hacks a single computer and tries to change the information in the blockchain, the rest of the network will reject it and preserve the genuine database because it wouldn't tally with their own copy. It would need consensus among the network for changes be made.
Protocol - a standardised method for achieving something.

So a permissionless distributed consensus protocol would be a standardised method for the various computers / nodes in a distributed network - where noone needs permission to be able to read/write changes to the data - to reach agreement about that set of data (e.g. whether to change it or not, what to change it to etc).
Or something like that.

Bitcoin is a permissioned blockchain, so would have permissioned distributed consensus protocols, although whether or how they might be different to permissionless ones I have zero idea.
Where this started for me was
DARPA(I was researching something else)
They mentioned that they wanted to have a workshop next Feb. and were seeking papers and information

According to the RFI, DARPA is particularly interested in “permissionless” distributed consensus protocols, which it describes as the protocols where any individual may join in the computation

"where any individual may join in the computation" would that mean that this site is blockchain based?
It would seem that they would be using blockchain technology, yes. The computation would presumably be by anyone with a computer who wants to do the work, and what they're looking for is protocols on how to make that secure and safe such that the only changes to the dataset are genuine.
I think that's what it's about, anyway. :)