# Glossary Atomic execution : The guarantee that a bundle's transactions land **in full and in order, or not at all**. A bundle with any failing transaction is dropped entirely. Auction tick : One 50 ms auction round in the Block Engine. Roughly eight fit into each Solana slot. See [Auction Mechanics](../concepts/auction-mechanics.md). Block Engine : Flowra's central service. It broadcasts the orderflow stream to searchers, validates and simulates bundles, enforces the validator's policy, runs the 50 ms auctions, and forwards winning bundles to the leader. See [Architecture](../concepts/architecture.md). Bundle : An ordered group of up to 5 signed transactions submitted as one atomic unit into the auction, carrying a tip. See [Bundles](../searchers/bundles.md). BundleStage : The validator client module that executes winning bundles atomically at the front of the block and runs the tip program crank each leader slot. Conflict-aware selection : Auction logic that detects overlapping account access between candidate bundles (write-write and read-write conflict; read-read does not) and selects the highest-value combination of non-conflicting bundles within the compute budget. CU reservation : The share of a block's compute units the validator reserves for auction bundles (configurable, 15% by default), released back to regular flow when no bundles are pending. Flowra Relayer : A TPU proxy that receives transactions on the validator's behalf, deduplicates them, and forwards them to the Block Engine and the validator, with no added packet delay. Flowra Validator Client : A validator client built on the Jito-Solana codebase (Agave lineage), extended with Flowra's bundle pipeline, CU reservation flags, and PBP policy push. Gulf Stream : Solana's mempool-less transaction forwarding design: transactions are pushed directly to upcoming leaders instead of gossiped publicly. The structural reason Solana's orderflow is dark by default. Leader / leader slot : The validator currently assigned to produce blocks, and its ~400 ms production window. MEV (Maximal Extractable Value) : Value extractable by controlling transaction inclusion and ordering: arbitrage, liquidations, and (in harmful forms) front-running and sandwiching. OOA (Open Orderflow Auction) : Flowra's market mechanism: a transparent, permissionless auction over pending-transaction flow. See [Open Orderflow & Accountability](../concepts/open-orderflow-auction.md). Orderflow : The stream of pending user transactions (swaps, liquidations, transfers) before finalization. See [Orderflow on Solana](../concepts/orderflow-on-solana.md). PBP (Programmable Block Policy) : Flowra's core feature: validator-defined block composition rules (address screening, program filters, MEV posture, priority pinning, compute quotas) owned by the validator as a policy file, pushed to the Block Engine, and enforced before the auction. See [PBP](../concepts/programmable-block-policy.md). PFOF (Payment for Order Flow) : Monetizing orderflow by routing it to paying market makers through exclusive channels; the model Flowra's open market replaces. Priority fee : The fee users attach to compete for inclusion. On Solana today, effectively a blind auction and a key source of systematic overpayment. Protocol fee : Flowra's 5% fee on auction tips; the remainder flows to validators and stakers. Sandwich attack : Harmful MEV where an attacker brackets a victim's trade with its own transactions to profit from induced price movement. Flowra's policy engine detects the wrapping pattern and lets validators reject it. Searcher : A participant running strategies over the orderflow stream and bidding tip-bearing bundles into the auction. See [Searchers](../searchers/index.md). SFDP (Solana Foundation Delegation Program) : The Foundation's stake delegation program; its rules influence which infrastructure validators can run without losing delegation. Slot : Solana's ~400 ms block production interval. State auction : The contest among bundles whose account footprints overlap. Each 50 ms tick resolves state auctions and assembles the winning batch from their winners. Tip : The searcher's auction bid, paid as lamport transfers to designated tip accounts inside the bundle and measured during simulation. Split 5% protocol / 95% validator and stakers. Tip account : One of the addresses returned by `GetTipAccounts`. Transfers to these accounts inside a bundle constitute the bundle's bid, claimed through the on-chain tip distribution mechanism.