Short answers, pulled from the story.
Apple released the Photos app for Mac as part of the OS X Yosemite 10.10.3 update on the 8th of April 2015. It replaced both iPhoto and Aperture, which Apple had announced in June 2014 it would discontinue.
Photos replaced Apple's two earlier programs, iPhoto and Aperture. Apple announced in June 2014 that it would discontinue both applications and replace them with Photos in 2015.
Photos was released for tvOS 10 on the 13th of September 2016, bringing it to the Apple TV. It came to visionOS after Apple introduced the Vision Pro headset at WWDC on the 5th of June 2023.
The iOS 18 and iPadOS 18 redesign, introduced at WWDC 2024, replaced the separate Library, Albums, and For You tabs with a single scrollable view. It also added natural language search and Apple Intelligence features such as the Clean Up tool, which removes distracting objects from photos.
iPhones save photos by default in the HEIF format, using a .heic file extension. HEIF offers smaller file sizes and higher quality than JPEG. JPEG, though, remains more widely compatible with older devices, and HEIF photos can be exported as JPEG files.
Critics said Photos removed functionality that iPhoto and Aperture had offered, including the ability to organize images into user-defined Events. Some customers who upgraded to OS X El Capitan without first updating iPhoto were locked out of that program entirely. Photos was their only remaining option, since iPhoto had been removed from the Mac App Store.