Apple has just released iOS 8.1.1, the fourth update to iOS 8 since it was released two months ago. The update is available for all devices running iOS 8, including the iPhone 4S, 5, 5C, 5S, 6, and 6 Plus; all iPads except the first-generation model; and the fifth-generation iPod Touch.
iOS 8.1 focused mostly on adding features like SMS forwarding and Apple Pay, but 8.1.1 returns the focus to fixing bugs. The biggest improvement should be better performance on the iPhone 4S and iPad 2, devices that both suffered when iOS 8 was originally released. While they aren't mentioned in the release notes, these performance improvements should hopefully apply to the original iPad Mini and the fifth-generation iPod Touch, since they both use hardware very similar to the 4S and iPad 2.
Apple usually gives some specific examples of other bugs that are being fixed, but it doesn't list any for this update—we'll update the article if we can find more information.
We'll be testing iOS 8.1.1 on some older hardware and reporting back with what we find soon. In the meantime, the update can be downloaded over the air or from iTunes—if your device doesn't have enough space to install the update, connecting it to iTunes is the best workaround.