Suffix

of Dexterity: +3-4 dexterity. (Seen on boots.)
of Brawn: +3-4 strength. (Seen on gloves.)

Suffixes come after Prefixes, as a type of item affix.

Diablo II Affixes

In Diablo II there were rules for item modifiers. Diablo III will not repeat these exactly, but there may be a continuation of some of the rules.

Magical items could have 1 prefix, 1 suffix, or both.
Rare items could have up to 6 affixes -- 3 prefixes and 3 suffixes -- though most had just 2-4 total affixes.
Crafted items had a few preset mods, and could roll up to 2 prefixes and 2 suffixes, though this varied slightly between recipes. Crafted items also had some Special Modifiers that were never found on magical or rare items.
Set Items and Unique Items were entirely custom designed, and could have any number of modifiers that didn't necessarily correspond to any of the affixes.

Nothing has been revealed about the organizing principles of itemization in Diablo III. We have seen a few in item hover descriptions, though.