# Glossary

## BUSY variable

The BUSY variable monitors the storing process of variables in the data storage. The BUSY variable is TRUE during the storing process and FALSE when the storing process is finished.

## 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.

## Function Block Diagram

Function Block Diagram (FBD) is a graphical programming language. A program is represented by directed networks. The elements represent function block instances, functions and variables. The connections represent the control flow.

## 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.

## Snapshot

A snapshot is the result of a backup process and saves the state of the device including all changes at the moment of saving.