Spotlight is Apples name for search in iOS and macOS. In iOS it can be activated by swiping down with one finger on the home screen, swiping right on the first home screen or by pressing ⌘ Space on an external keyboard.
Spotlight can be used to search for apps, documents, Contacts, email, music, movies, do web searches, calculate math, convert currencies and units, among other things.
Settings for Spotlight can be found in Settings > General > Spotlight Search. There you can decide what apps to allow search in.