Here are the definitions of the three terms, taken word-for-word from Looking at Movies: An Introduction to Film (W.W. Norton & Co, 2006; http://www.wwnorton.com/college/film/movies2/glossary.aspx).
real time: The actual time during which something takes place. In real time, screen duration and plot duration are exactly the same. Many directors use real time within films to create uninterrupted "reality" on the screen, but they rarely use it for entire films. Compare cinematic time, stretch relationship, and summary relationship.
stretch relationship: A time relationship in which screen duration is longer than plot duration. Compare real time and summary relationship.
summary relationship: A time relationship in which screen duration is shorter than plot duration. Compare real time and stretch relationship.
Alongside those definitions, this source identifies a fourth...
(The entire section contains 426 words.)