Adam Clarke on Exodus 29:2

Unleavened bread - Three kinds of bread as to its form are mentioned here, but all unleavened:

1. מצות matstsoth, unleavened bread, no matter in what shape. See Exo 12:8.

2. חלת challoth, cakes, pricked or perforated, as the root implies.

3. רקיקי rekikey, an exceeding thin cake, from רק rak, to be attenuated, properly enough translated wafer. The manner in which these were prepared is sufficiently plain from the text, and probably these were the principal forms in which flour was prepared for household use during their stay in the wilderness.

These were all waved before the Lord, Exo 29:24, as an acknowledgment that the bread that sustains the body, as well as the mercy which saves the soul, comes from God alone.