Expanded two phase commit entry.

Signed-off-by: Dj Walker-Morgan <[email protected]>

product_docs/docs/pgd/5/terminology.mdx

@@ -115,7 +115,8 @@ A PGD cluster is based around bidirectional replication, but in some use cases s
 
 #### Two-phase commit (2PC)
 
-A multi-step process for achieving consistency across multiple database nodes.
+A multi-step process for achieving consistency across multiple database nodes. A first phase sees a transaction prepared on an originating node and sent to all participating nodes. Each participating node validates that it can apply the transaction and 
+signals its readiness to the originating node. This is the pre-commit or prepare phase. In the second phase, if all the participating nodes signal they are ready, the originating node proceeds to committing the transaction and signal the participating nodes to commit too. This is the commit phase. If, in the pre-commit phase, any node signals it is not ready, the entire transaction is aborted. It's this process that ensures all nodes get the same changes.
 
 #### Vertical scaling or scale up