![1girl absurdres androgynous astolfo_(fate) bad_link black_legwear boots braid cape drawfag fate/apocrypha fate/grand_order fate_(series) fingerless_gloves flat_chest fur_trim genderswap genderswap_(mtf) gloves highres multiple_views pink_eyes pink_hair reverse_trap smile standing sword thighhighs weapon white_footwear rating:s score:15 post #3065972](/cdn_image/preview/3a/73/3a7316133dc079691b32d0d939dd2279.jpg)
Per trap, a female character who looks and may or may not act masculine. Most likely also dresses like a male, although unlike mere crossdressing the character is assumed by others to be male until demonstrated otherwise.
As a rule of thumb, if you can correctly tell the gender with complete certainty from the thumbnail alone, it's not a reverse trap.
Often indicated on Pixiv by the 男装 (Dansou lit. "Disguising oneself as a man") and 男装の麗人 (Dansou no Reijin lit. "A beautiful woman disguised as a man") tags. See also tomboy, which may overlap. pool #6118 may also overlap in some places, but is not necessarily the standard.