Swift (no relation to OpenStack Swift or Tom Swift or Taylor Swift; and apparently also unrelated to the parallel scripting language Swift) is a programming language announced by Apple in 2014 as a new language for use in developing apps for iOS or OS X. It is able to coexist with the previous main language for this use, Objective-C, through the use of "bridging headers" that are read by both languages and allow classes from each language to be accessed from the other.
Swift appears to borrow syntax elements from a number of other programming languages. It uses curly braces to mark blocks like the C family of languages, but does not use semicolons between statements (except when multiple statements are on the same line). Some other syntax and keywords resemble BASIC and Pascal, among other languages. It also has an instant-gratification interpreted mode to try out program statements in real time, like Python; Swift (as implemented in the Xcode environment on OS X) has a "playground" to test out programming constructs without needing to build an entire app. An introductory book on the language can be downloaded free through iTunes, but in a format that is only readable on Apple devices.
People testing Swift (available as of June 2014 in a beta version of Xcode released to members of Apple's developer program) found it to be something less than swift at some sorts of number-crunching; sorting a large array of integers, for instance, took much longer than in other languages including Objective-C and Python. This was possibly due to there not being as much optimization in the early beta version as were present in later release versions. Since its initial release, Swift has gone through a number of revisions, some of which included changes that broke earlier Swift code.
In December 2015, Swift was made open-source.