Perhaps it's a simple question, yes, but this time of year you're bound to see many jackets described alternately as "herringbone" or "tweed" blazers. So, after fielding multiple queries on the subject since tweed season began, our men's editor has decided to explain the difference in writing, for once and for all.
TWEED: FABRIC. Tweed is a woolen fabric, usually made with yarns that are rough and unfinished to create that coarse feel to the hand and the rustic look above that makes the fabric appropriate for outerwear and rugged blazers. To create tweed, the yarns can be woven in either a plain weave (which is flat) or twill (which has diagonal ribs).
HERRINGBONE: PATTERN. It's created from weaving twill in a way that results in rows of those characteristic V's you see above. The pattern gets its name from its resemblance to the bones of herring fish.
Simple, enough, right? Here's where it gets more complicated: plenty of tweed garments are, in fact, woven in a herringbone pattern, but the two don't necessarily go hand in hand. If you're not sure your herringbone jacket is tweed, check the label to make sure it's wool—then feel the jacket for the slightly rough, coarse feel that makes this fabric special.