Entrañas literally translates to "entrails" or "bowels", but in Spanish, it is beautifully used as a metaphor for the deepest, most profound part of your soul or emotions.
In the song, Maluma sings, "Hablo de mis entrañas para ser sincero" (I speak from my core to be honest). He uses this highly visceral word to express that he is completely baring his soul and speaking from the absolute bottom of his heart about his past mistakes.
Colombian star Maluma strips away his usual party-ready swagger for something deeply remorseful in "Marinero". The title means "Sailor," and he uses that metaphor to describe his past bad behavior: while his partner gave him her whole heart, he was drifting from port to port looking for casual love ("Yo era un marinero buscando amor / Iba por cada puerto como si nada" [I was a sailor looking for love / I went from port to port like it was nothing]). Instead of finding freedom, he admits that the more waves he chased, the more he shipwrecked ("Entre más olas, más naufragaba").
He doesn't sugarcoat his own faults at all. He bluntly confesses that he only cared about physical intimacy in the past ("Sólo desnuda era que me gustabas" [I only liked you when you were naked]) and even admits to cheating back when she was already graduated and he was still in school ("Tú ya graduada y yo en el colegio... Y practicaba con otras cuando no estabas" [You were already graduated and I was in school... And I practiced with other girls when you weren't around]). Now, he is drinking alone, facing empty rooms filled with "silences that scream goodbye," and finally letting her go so she can find happiness with someone else.