Heart Container is an item present in nearly every Zelda game. It often appears right after Link defeats a boss and permanently adds one heart to Link's health capacity, completely restoring Link's health in the process.
Pieces of Heart are another kind of item. After collecting a certain number of them, usually four, a Heart Container will be formed.
Related ThreadsHeart Container Question - last post by @ Jun 30, 2008
Heart Containers - last post by @ Aug 9, 2004
Heart Container/Potion - last post @ Jan 19, 2014
The Full Heart Container You Receive From The Minish - last post by @ Mar 20, 2007
Heart container with neptoona? - last post by @ Aug 26, 2009