off flavor

Some contents overlapping with the previous post are omitted. 
Original content is from morebeer.com

Alcoholic

tastes: paint thinner, acetone, undesirable hot
causes: fusel alcohol(propanol, butanol, isobutanol), isoamyl alcohol, phenolic alcohol(tyrosol). fermenting at too hot temperature, keeping beer on the trub for too long, oxidation

Astringent

tastes: vinegary, tannin, drying, puckering
causes: polyphenol, tannins(skins or husks of grain), steeping grain for too long, grain was excessively crushed/milled, mashing pH exceeds 5.2-5.6, over-hopping

Chlorophenol

tastes: plastic, iodine
causes: brew or rinse with chlorinated tap water, cleaner or sanitizer, wild yeasts

Cidery

tastes: apple cider, acetaldehyde
causes: use too much corn or cane sugar, acetaldehyde

Estery(fruity)

tastes: banana, pear, strawberry, raspberry, grapefruit
causes: a by-product of fermentation. under pitching or high fermentation temperatures, low oxygen level

Grassy

tastes: cut grass, musty
causes: grain or extract contaminated by mold or bacteria, aldehyde, incorrectly processed hop

Husky(grainy)

tastes: raw grain
causes: over milled grain, highly toasted malts

Medicinal

tastes: cough syrup, mouthwash, band-aid, smoke, clove-like spicy
causes: phenols, incorrect mashing and sparging pH, water amounts and temperatures, improper sanitizing with chlorine and iodine, yeast

Moldy

tastes: mold
causes: storing fermenting beer in a damp, dank area, contaminated grain or extract

Salty

tastes: salt
causes: too much gypsum or Epsom salt

Soapy

tastes: soap, detergent, oily, fatty
causes: keeping beer in the primary fermentation for too long(fatty acids in the trub start to break down)

Solvent-like

tastes: paint thinner, nail polish remover
causes: a combination of very high fermentation temperature and oxidation, using not food-grade plastic

Sweet

tastes: overly sweet, sugary, cloyingly sweet
causes: stuck fermentation, yeast with a low tolerance for alcohol in high gravity beer, a sudden drop in temperature, lacking hop bitterness, too much flavoring or adjuncts

Yeasty

tastes: yeast, bready, sulfur-like
causes: unhealthy or mutated yeast, sitting on dead yeast for too long(autolysis), not flocculate completely, incorrect serving manner