Thighs that are drawn thicker than what is deemed "normal."
Compare post #1694328 ("normal" thighs) with post #1557661 (thick thighs).
In accordance with the above, don't make the common mistake of adding this tag to posts just because thighs are simply visible at all; there needs to be actual large size for this tag to qualify. Generally speaking, if each thigh is at least as large around as the character's waist, they may be considered thick, though be mindful of cases where a character has either a very thick waist (the thighs need not be that thick) or a very thin waist (the thighs would need to be considerably thicker).
The following tags are aliased to this tag: thunder_thighs, fat_thighs, big_thighs, and thighthick (learn more).
This tag implicates thighs (learn more).