PaRDeS
The four level of interpretation are called: Parshat, Remez, D’rash & Sod. The first letter of each word P-R-D-S is taken, and vowels are added for pronunciation, giving the word PARDES (meaning "garden" or "orchard"). Each layer is deeper and more intense than the last, like the layers of an onion.
P'shat (pronounced peh-shaht' - meaning "simple")
The p'shat is the plain, simple meaning of the text.
Remez (pronounced reh-mez' - meaning "hint")
This is where another (implied) meaning is alluded to in the text, usually revealling a deeper meaning.
D’rash (pronounced deh-rahsh' also called "Midrash")
This is a teaching or exposition or application of the P'shat and/or Remez.
Sod (pronounced sawd or sood [like "wood"] - meaning "hidden")
This understanding is the hidden, secret or mystic meaning of a text