Backend terms you can return to

You do not need to memorize these terms. Return when a lesson uses a word you cannot connect to a concrete action.

Requests and identity

Term	In Taskboard
HTTP contract	The method, path, input, status, and response the browser can rely on.
Middleware	An Express function that handles part of a request before the route runs.
Authentication	Finding the user from a valid stored session.
Authorization	Checking whether that user can perform this action in this workspace.
Session	A server record identified by an opaque cookie token.
CSRF	A forged request that tries to use someone else's browser session. Taskboard requires a separate token for authenticated mutations.
Tenant	One workspace whose data belongs together and stays separate from other workspaces.

Stored data

Term	In Taskboard
Migration	A committed change to the Postgres schema.
Constraint	A database rule that rejects an invalid row, such as a task referencing another tenant's project.
Transaction	Changes that commit together or roll back together.
Isolation	Rules for what concurrent transactions can observe.
Row lock	A transaction holds a workspace row while deciding a shared quota or permission change.
Optimistic concurrency	An edit supplies the version it read. A conflicting version makes the server reject the edit.
Keyset pagination	The next page starts after a stable timestamp and ID pair.
Connection pool	Reusable database connections shared by requests and jobs.

Work and failures

Term	In Taskboard
Idempotency	Retrying one keyed task creation returns its saved result instead of creating another task.
Outbox	The transaction stores a job beside its domain changes so committed work is not lost before delivery.
Lease	A temporary job claim. Another worker can recover it after expiry.
Fencing token	A claim identifier checked before renewal or completion. An old worker cannot acknowledge a newer claim.
At-least-once delivery	A job can run more than once after an uncertain failure. SMTP email can be duplicated.
Backoff	Wait longer between retry attempts, with random jitter to spread retries.
Webhook	An external provider sends an HTTP event to the app.
Reconciliation	Fetch current provider state and repair the local billing view.
Readiness	Whether the process can serve traffic with its required migrations applied.
Liveness	Whether the process is alive enough to respond.
Observability	Logs and metrics that show what the running system is doing.
RPO	How much recent data a recovery plan can afford to lose.
RTO	How long that recovery can take.

A term describes a mechanism. The lesson explains why that mechanism matters and what it cannot guarantee.