![1boy 1girl :3 :d ahoge aura_bella_fiora bangs blonde_hair blue_eyes blunt_bangs brother_and_sister brown_gloves cape commentary_request copyright_name crossdressing gloves green_cape green_eyes hair_between_eyes heterochromia jewelry k-ta long_sleeves looking_at_viewer mare_bello_fiore necklace open_mouth otoko_no_ko overlord_(maruyama) pants photoshop_(medium) pleated_skirt pointy_ears reverse_trap short_hair siblings simple_background skirt smile twins white_background white_gloves white_pants rating:s score:1 post #3205997](/cdn_image/preview/95/d4/95d4da48b23f02107888363006e557eb.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.