# Glossary

## certificate authority (CA)

A certificate authority (CA) issues digital identity certificates in a public key infrastructure.

## certificate signing request (CSR)

A certificate signing request (CSR) is made by an applicant to a certificate authority in order to apply for a digital identity certificate.

## flow

In Node-RED, a flow is a connected subgraph of nodes with its own data sources and data sinks. Flows may be interconnected via indirect links.

## message

In Node-RED, messages are JavaScript objects, that are passed between the nodes of a flow. Messages usually have a set of properties whose values can be any valid JavaScript type.

## node

Nodes are the core elements in Node-RED. Nodes function as black boxes, that take in data as messages. These messages are transformed by the node and output again.

## Node-RED

Node-RED is a flow-based programming tool for transferring and manipulating data from devices, APIs or online services. With Node-RED, a program is represented as a directed graph. The nodes represent transformations. The connections represent the data flow.

## OPC UA Server

An OPC UA Server exposes services for OPC UA Clients, enabling machine-to-machine communication in industrial automation.

## Program Organisation Unit (POU)

Program organisation units contain a defined portion of a program and provide a defined interface with inputs and outputs. Functions, functions blocks and programs are program organisation units.

## real-time application

The real-time application controls the devices connected to the controller and handles their process data in real-time. The real-time application is programmed in accordance with IEC 61131-3.

## SSH File Transfer Protocol (SFTP)

The SSH File Transfer Protocol also called Secure File Transfer Protocol allows to exchange files between two hosts.