If you want to see the lyrics of the song that's playing now, you can install a plugin in your favorite player. But if you want the lyrics displayed on top of any application, you will need one of these utilities.
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MiniLyrics (Windows, macOS, Android)
MiniLyrics is a free plugin for displaying the text of the current song. It supports popular desktop and mobile players: iTunes, Windows Media Player, Winamp, and many others.
The plugin automatically searches and downloads lyrics. In addition, you can save the text to a file and view it at a convenient time. Skins support transparency, so you will be able to work with any application and see the lyrics at the same time.
Musixmatch Lyrics (Windows)
Musixmatch will automatically display the lyrics when playing Spotify, iTunes, Windows Media Player. The text moves along with the song, so you don't have to scroll and find the needed fragment.
The text is in a small separate window which can be positioned as you wish.