Parallax creates, stores and transfers large volumes of data. This data must get formatted in standardized and memory-efficient ways to allow anyone to run a node on relatively modest consumer-grade hardware. To achieve this, several specific data structures are used on the Parallax stack.
You should understand the fundamentals of Parallax and client software. Familiarity with the networking layer and the Ethereum whitepaper is recommended.
Patricia Merkle Tries are structures that encode key-value pairs into a deterministic and cryptographically authenticated trie. These are used extensively across Parallax.More on Patricia Merkle Tries