It looks like you're referring to a release tag for a specific download of the TV show , specifically the Season 1 finale episodes 23 and 24 ("The Woman" and "Heroine").
: Combining E23 and E24 ensures you get the full story arc of the finale without missing the transition between the two parts. _DLMux_720p_-_-_Ita_Aac_Elementary_S01E23-24_-_...
Since "Solid Post" is often used in the scene to confirm a high-quality or working upload, It looks like you're referring to a release