A constraint is a condition that has to be fulfilled in a given context. Constraints are typically used in databases and programming languages to detect errors, ensure data consistency, accuracy, and to enforce business requirements.

DO NOT USE if your question relates to one or two components of the tidyverse, such as dplyr or ggplot2. Use *those* tags, and tag with `r` as well for a better response.

Global variables are variables that are accessible from all elements of a software component.

AppleScript is an end user scripting language that has been available in Mac computers since System 7 Pro (7.1.1). It allows for automation of system tasks, communication between processes, and creation of workflows, amongst other functions.

Questions specifically for version 5.x of the Qt library. If your question applies to other versions of Qt, use the tag [tag:qt4] or [tag:qt3]. It is recommended to use with the tag [tag:qt].

A type of relationship between entities of types A and B which associates a list of entities of type B to an entity of type A and vice versa. Types A and B may be the same type.

Mocha.js is a feature-rich JavaScript test framework running on Node.js and the browser.

Celery is a distributed task queue framework for Python, used for asynchronous and parallel execution.

The Python Imaging Library (PIL) provides the Python language with a de-facto standard foundation for image work. PIL’s API is lightweight but semantically consistent; it furnishes a range of comfortably Pythonic tools throughout much of the imaging lexicon: processing, analysis, compression and codec abstraction, etc. – all of which builds upon a bespoke and readily extensible library structure.

A design pattern that ensures that exactly one application-wide instance of a particular class exists. One of the Gang of Four's creational design patterns.

In GUI (inc. web page) context, alignment refers to the positioning of visual elements. Or for memory addresses, being a multiple of some power of 2.