SUMIFS is an Excel function, introduced with Excel 2007 (v12.0), which allows for the summation of values selected according to several criteria – addition is only of cells meeting all the conditions.

Deferred objects simplify callback management in an asynchronous environment, mitigating the "Pyramid of Doom" that results from too many levels of nested callbacks.

This tag is used for question related to the session bean and message-driven bean component types of the EJB 3.1 programming model.

The same origin policy, which is enforced by Web browsers, limits JavaScript in a document loaded from one origin from accessing data from another origin. The limitation can be relaxed using the CORS protocol.

In object-oriented programming, a metaclass is a class whose instances are classes. Just as an ordinary class defines the behavior of certain objects, a metaclass defines the behavior of certain classes and their instances. Not all object-oriented programming languages support metaclasses.

A weak reference is a one that makes no claim of ownership. A weak reference keeps a reference to the object in question while it is in memory, but does not prevent the memory management system from reclaiming the associated memory when the referenced object is otherwise no longer needed. Many languages feature or support various levels of weak references, such as Swift, Objective-C, Java, C#, Python, Perl and Lisp.

On macOS 10.4+ and iOS 3.0+, an instance of NSFetchRequest describes the search criteria used to retrieve data from a persistent store. It is a class in the Apple Core Data Framework.

This is the Symfony 2.1.x specific tag. Use it in addition to the symfony2 tag if your question is specific to Symfony 2.1.x — not just 2.x.

Consul is a tool for discovering and configuring services in the infrastructure.

HealthKit is a framework for iOS and watchOS that allows health and fitness services to share their data with the new Health app and with each other.

Kusto Query Language (KQL). Use this tag with any questions or advice of operator, complicated query, performance challenges or missing capabilities. KQL is a read-only request to process data and return results. The request is stated in plain text, using a data-flow model designed to make the syntax easy, author and automate. The query uses schema entities that are organized in a hierarchy similar to SQL's: databases, tables, and columns.