Soliá is a cool, stylistic contraction of the word solita (all alone). It's a prime example of the informal, catchy slang you'll hear in modern reggaeton.
Solita is the diminutive of sola (alone), which softens the word. In the song, Bad Bunny uses soliá to paint a picture of a woman who has left a bad relationship and is confidently going out by herself, ready to have fun and be independent.
In "Soliá", Puerto Rican superstar Bad Bunny watches a girl step into the club completely alone—"Llegó soliá, salió sin las amigas" ("She arrived all alone, she went out without her friends"). The title itself drops the final 'd' from soliada or sola, mirroring how people talk on the street. She is fed up with an untruthful partner, drinking to escape "esa relación de mentira" ("that fake relationship"), and she is "casi soltera" ("almost single"). Benito spots her eye contact right away and gives her partner a blunt warning: send him a text telling him not to leave her alone, because if he does, he might never get her back.
Bad Bunny leans into petty, funny modern romance tropes that hit hard. When she posts a clip on her social media, "alguien se picó" ("someone got pissed off / jealous"). He drops a pop-culture punchline to explain why she is done taking orders from her ex: "la Kardashian ya no está pa' Kanye" ("the Kardashian is no longer into Kanye"). After dealing with endless lies, she has zero patience left to give him another chance. Instead, she just wants to dance until the windows fog up ("que los cristales se empañen") and end the night on her own terms with Benito.