Port
A port is a named, typed connection point on a block. Input ports state what a block needs; output ports state what it produces. A connection is only valid between an output and an input whose data types agree, which is how a flow is checked for correctness before it ever runs.
What it means
Port types name the shape of the data travelling on a wire: text, json, vector, blob, the trigger signal a flow starts on, or the permissive any. Two ports are compatible when their types match, or when one side is deliberately untyped. Wiring a json output into a text input is not a run-time surprise — the composer refuses it on the canvas.
How SwiftTune uses it
Each port is drawn with its name and its data type next to the handle — both in the mono face, because both are identifiers — and coloured by type, so a flow can be read at full zoom without opening a panel. A rejected connection stays visible in red with the reason attached, rather than disappearing and leaving you to guess what the editor objected to.