Q-Digest is simply a complete binary tree over the range of values, where the leaf nodes are the values themselves. It as an algorithm for computing approximate quantiles on a collection of integers. Data quantiles have many applications from robust estimation, which I'll return to in a later article, to improving database query planning. A quantile summary of the sort the q-digest algorithm generates, captures information about the cumulative density function of a random variable and as such can be used for non-parametric estimation.

QGIS is an open source Geographic Information Sytem, that allows you to create, edit, visualize, analyze and publish Geospatial information on Windows, Linux and Mac operating systems.

QlikView is the most flexible Business Intelligence platform for turning data into knowledge. It creates endless possibilities of making ad hoc queries in a non-hierarchical data structure. It is possibe due to AQL (Associative Query Logic) for automatically associating values in the internal QlikView database. QlikView simplifies analysis and makes it possible for anybody to create very useful, accurate KPI, measurement reports and performance dashboards and make accurate, strategic decisions.

Qlik Sense is a sales management and data analytics application that gives you sales, profit and loss reports displayed in colourful and customizable charts and sheets. Qlik Sense lets you build dynamic dashboards and personalized reports for individuals in your company which in turn promote meaningful insights as well as visuals. Furthermore, Qlik Sense helps identify areas of financial crisis and potential from within your enterprise.

QlikView is a PC-based desktop Business Intelligence tool from Qlik. Unlike other traditional BI tools it follow MVC architecture.

A mobile operating system that was originally developed for embedded systems.

QR code (abbreviated from Quick Response Code) is the trademark for a type of matrix barcode (or two-dimensional barcode) first designed for the automotive industry in Japan. A barcode is an optically machine-readable label that is attached to an item and that records information related to that item. The information encoded by a QR code may be made up of four standardized types ("modes") of data (numeric, alphanumeric, byte / binary, kanji) or, through supported extensions, virtually any type of data.

HP QuickTest Professional (QTP) provides functional and regression test automation for software applications and environments. It uses Visual Basic (VBScript) scripting language to specify a test procedure, and to manipulate the objects and controls of the application under test.

A chip with four independent units (cores) that read and execute CPU instructions such as add and move data. The individual cores can run multiple instructions simultaneously, increasing the speed for programs compatible with parallel processing.

A multicopter that is lifted and propelled by four rotors. Quadrotors are classified as rotorcraft, as opposed to fixed-wing aircraft, because their lift is generated by a set of revolving narrow-chord airfoils. 

A quadruple-play network is one that offers mobility in addition to the voice, data and video provided by a triple-play network.  

Any systematic process of checking to see whether a product or service being developed is meeting specified requirements. It results in an increase in customer confidence, company's credibility, and work processes and efficiency.

A procedure or set of procedures intended to ensure that a manufactured product or performed service adheres to a defined set of quality criteria or meets the requirements of the client or customer.

The translation of user requirements and requests into product designs. The goal of QFD is to build a product that does exactly what the customer wants instead of delivering a product that emphasizes expertise the builder already has.

A quality management system (QMS) is a set of policies, processes and procedures required for planning and execution in the core business area of an organization. It is a system by which an organization aims to reduce and eventually eliminate nonconformance to specifications, standards, and customer expectations in the most cost effective and efficient manner. ISO 9001:2008 is an example of a Quality Management System.

A measure of the overall level of customer satisfaction with a vendor. QoE is related to but differs from Quality of Service (QoS). It expresses user satisfaction both objectively and subjectively.