Update glossary.asciidoc

Added new terms

glossary.asciidoc

@@ -171,6 +171,9 @@ Eclair::
 encoding::
     TBD.
 
+Electrum Server::
+    An Electrum server is a bitcoin node with an additional interface (API) is often required by bitcoin wallets that do not run a full node. For example, these wallets check the status of specific transactions or broadcasts transactions to the mempool using Electrum sever APIs. Some Lightning wallets also use Electrum servers, so even if they are non-custodial, they may compromise user sovereignty in that users trust the Electrum server to provide accurate information and privacy in that calls made to the Electrum server may reveal private information. 
+
 Ephemeral Key::
     Ephemeral keys are mainly within the SPHINX Mix Format and Onion Routing on the Lightning Network.
     They are generated for each execution of the routing process.
@@ -224,6 +227,9 @@ Hash Function::
 hashlocks::
     A hashlock is a type of encumbrance that restricts the spending of an output until a specified piece of data is publicly revealed. Hashlocks have the useful property that once any hashlock is opened publicly, any other hashlock secured using the same key can also be opened. This makes it possible to create multiple outputs that are all encumbered by the same hashlock and which all become spendable at the same time.
 
+HODL/Hold Invoices::
+    HODL/Hold invoices are effectively standard HTLC LN invoices with the exception that the recipient can “hold” the funds, deferring to settle the transaction until some condition has been met. The sender remains committed unless the recipient opts to cancel the transaction. 
+
 HTLC::
     A Hashed TimeLock Contract or HTLC is a class of payments that use hashlocks and timelocks to require that the receiver of a payment either acknowledges receiving the payment prior to a deadline by generating cryptographic proof of payment (usually called the preimage of the payment hash) or forfeits the ability to claim the payment, returning it to the payer.
     On the Lightning Network HTLCs are outputs in the commitment transaction of a payment channel and are used to enable the trustless routing of payments.
@@ -272,6 +278,9 @@ Noise_XK::
     Encryption to a known recipient, strong forward secrecy. This payload is encrypted based on an ephemeral-ephemeral DH as well as an ephemeral-static DH with the recipient's static key pair. Assuming the ephemeral private keys are secure, and the recipient is not being actively impersonated by an attacker that has stolen its static private key, this payload cannot be decrypted. Sender authentication resistant to key-compromise impersonation (KCI). The sender authentication is based on an ephemeral-static DH ("es" or "se") between the sender's static key pair and the recipient's ephemeral key pair. Assuming the corresponding private keys are secure, this authentication cannot be forged.
     // the noise protocol documentation is according to their IPR section public domain. The author is Trevor Perrin (noise@trevp.net)
 
+Neutrino::
+    Neutrino is a later alternative to SPV that also verifies whether certain transactions are contained in a block without downloading the entire block. However, it offers a number of improvements over SPV: Neutrino does not transmit any information that would allow a third party to determine users’ identities, it facilitates the use of non-custodial apps, and it reduces the computational load on full nodes. The tradeoff for these improvements is that Neutrino requires more data from the full node than SPV.
+
 Onion Routing::
     Onion routing is a technique for anonymous communication over a computer network.
     In an onion network, messages are encapsulated in layers of encryption, analogous to layers of an onion.
@@ -424,6 +433,9 @@ SPHINX Mix Format::
     While the privacy of the sender and receiver of the payment is protected, each node is still able to return an error message along the path to the originator of the message.
     The paper can be found at https://cypherpunks.ca/~iang/pubs/Sphinx_Oakland09.pdf
 
+Submarine Swaps::
+    Submarine Swaps enable transfers between on-chain addresses and off-chain locations, like the LN. Just as standard LN transfers chain payments by means of HTLCs that make the final claim on funds conditional on the recipient revealing a secret to all links in the chain, Submarine Swaps use the same logic and procedure to transfer funds across the on-chain/off-chain barrier with minimal trust. They can also be used to enable transfers from another chain, say Litecoin, to an off-chain LN address. Reverse Submarine Swaps allow bitcoin transfers in the opposite direction that is, from an off-chain LN location to an on-chain address.
+
 timelocks::
     A timelock is a type of encumbrance that restricts the spending of some bitcoin until a specified future time or block height. Timelocks feature prominently in many Bitcoin contracts, including payment channels and hashed timelock contracts.