There's no single place to look up definitions of terms that get thrown around. Presumably "LSA" stands for "loan signing agent", which how some mobile notaries describe themselves. Other phrases are "notary signing agent" or just "signing agent".
In some documents in a real estate package you may see "closing agent" to refer to the notary. But in other documents "closing agent" means what is described in the Closing Disclosure as the "settlement agent", the firm that receives funds and documents into escrow and, during the closing process, disburses funds to those who are owed money, gets documents recorded, and sends documents to those who are entitled to them.