Glossary

Words on this page mean something particular inside Twill, which is not always what they mean elsewhere in Roblox development. Anything not listed here means what it usually does.

Structure and boot

Term	What it means
Service	A server-side ModuleScript returning a table, discovered by Lifecycle. Every field is optional, so a module with none of them is still a legal service. See Write a service.
Controller	The client-side counterpart of a service, booted by the same Lifecycle. Identical in shape, named separately so it is always clear which side a module runs on. Lifecycle itself draws no distinction and types both as Service. See Write a controller.
Server half	ServerScriptService.Twill. Never replicated. It holds more than secrets: thresholds, the metering algorithm, each player’s current allowance, and all data handling.
Root table	ReplicatedStorage.Twill, which resolves modules by name on first use. Naming a server-only module from a client fails there rather than handing back nil.
Init	The first boot phase. Runs sequentially for every service. Your own state only, because another service may not be set up yet.
Start	The second boot phase, after every Init has finished. Connect, listen, and call other services freely. Each Start runs on its own thread, so boot order decides when one begins, never the order in which they finish.
Priority	A number on a service deciding boot order. Lower boots first, and ties break by name so the order is stable across runs.
Critical	A flag on a service whose failed boot locks the server and refuses every player, rather than serving a game that is quietly missing a system.
Player pipeline	The path a joining player takes: the gate holds them, then every service is announced through OnPlayerReady in boot order. Server-side only, because on a client PlayerAdded means somebody else joined.
Gate	A function that holds a joining player until something finishes, normally until their data is loaded. Installed with Lifecycle.SetPlayerGate.

Cleanup and lifetimes

Term	What it means
Bag	A Twill.Bag, usually handed out by Scope. You put what you made into it, and the framework closes it. Closing runs newest first and always runs to the end.
Player bag	Closes when that player leaves. Handed to every service as the third argument of OnPlayerReady, which is why most code never calls Scope directly.
Character bag	Closes when the character model is removed, which Roblox does at respawn, not at the moment of death. For anything that should outlive dying, such as a ragdoll.
Alive bag	Closes the instant the humanoid dies, or on removal if the character is taken away without dying. For anything that should stop while a player is dead: movement, abilities, input.
Owner	The bag passed as the last argument to a Twill function that starts something lasting. Whatever was started closes with it.
Framework bag	Scope.Framework(), which lives as long as the session. Anything in Twill that starts a connection without an owner puts it here, because nothing in the framework is allowed to start a connection nobody owns.

Player data

Term	What it means
Template	The shape a new profile starts as. Fields missing from an existing profile are filled in from it on load, so adding a field later needs nothing else.
Migration	A function keyed by the version it produces, so [2] upgrades a version 1 profile. They run in ascending order and only on profiles that already hold data.
Branch	A separate store for player data that does not need loading on every join, with its own template, version, and migrations. See Data.
Scope (data)	The name of one store belonging to a user: "main" for the primary profile, or a branch name. Used by Data.Edit, Data.Reset, and the admin console.
Session	Store’s hold on a key. One server at a time, which is what stops two servers writing over each other. Losing it mid-play costs the player their place on that server rather than their progress.
Outcome	The typed value returned by Data.Edit and Data.Reset, naming what actually happened instead of a boolean that hides the reason.
Validate	A check you give Data or Store. A save it refuses is skipped and the last good data stays stored, and an edit it refuses returns the outcome refused.
Storable shape	Data a DataStore can hold and return unchanged. The traps are silent: a table mixing named and numbered keys, and gaps in a numbering, both come back wrong with no error. Serialize.FindUnstorable names them.

Three different things are called a scope. A data scope names a store, such as "main". A Log scope is the label on a logger, such as [Shop]. Twill.Scope is the cleanup module, which deals in bags and neither of the other two. They never appear in the same argument, but the word is overloaded.

Networking and replication

Term	What it means
Wire id	The number the server assigns to a remote. A client-declared remote receives it a moment later; a call made before then is held and sent once it arrives.
Signature	The rendering of a remote’s argument and reply types. Declaring one name with two different signatures is refused, because the alternative is one caller encoding through another’s types.
Frame	One call inside a message, carrying the length of its own body. That length is why a corrupt or refused call costs only itself.
Reject	What a refused caller is told. Required on a remote that replies, since a refusal without one leaves the caller waiting.
Token bucket	A meter that refills at its rate and never holds more than its burst. A rate below one is how you spell a cooldown.
Throttle (Limit)	A function that answers how many were held back since it last spoke, and nil in between. It exists so that logging does not amplify the flood it is refusing.
Key (replication)	The top-level name a value is published under. It cannot contain a dot, because the first dot separates the key from the path inside it.
Path	Everything after the first dot in a replication address or a Data.Edit call. In "Data.Stats.Coins", Data is the key and Stats.Coins is the path.
Patch	The difference between what a client was last sent and what it should hold now. Only what moved travels, so changing one field deep inside a large table sends that field rather than the table.
Replicated field	A field named in Data.Replicate, which reaches its owner’s client under the Data key and follows direct mutation. Only the named fields travel, and only to their owner.

Permissions, draws, and tokens

Term	What it means
Rank	A number you name yourself. Higher means more authority. It reaches the client as a player attribute, read-only there, so hiding a button by rank is safe while trusting a client’s claim about one is not.
Fail closed	Answering with a refusal when a check cannot be completed, rather than with the unchecked value. Filter returns nil when the Roblox filter is unreachable, never the text that went in.
Commitment	A digest published before a draw is made, proving the outcome was fixed in advance. See Random.
Round	The object returned by Random.Commit(). It carries a commitment, draws from a reproducible stream, and can reveal its seed for auditing.
Budget (Shared)	This server’s allowance for publishing, subscribing and memory store requests, counted per minute by Shared.
Ticket (Teleport)	The signed claim a teleported player carries. It names the data waiting in a memory store, which never passes through the client.
Audience	A string signed into a token and checked when it is read, so a token minted for one purpose is refused by every other.