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.
This song is a brutally honest confession from someone who messed up a good relationship. Maluma isn't making excuses here; he's laying it all out. He admits he was the problem, singing, "Sé que fui el culpable, por eso te pierdo" (I know I was the guilty one, that's why I'm losing you). He even says that while his partner was talking, he wasn't listening because, "Sólo desnuda era que me gustabas" (I only liked you naked). Ouch. That's a pretty cold thing to admit.
The whole song is built around a powerful metaphor. While his partner was giving him her heart, he saw himself as a sailor, or "un marinero buscando amor" (a sailor looking for love). He was going from port to port, treating it like nothing. But the clever part is the twist: "Entre más olas, más naufragaba" (The more waves, the more I shipwrecked). All his playing around didn't lead to freedom or fun, but to his own emotional wreck. Now he's left with regret, realizing that when he finally tried to come home, "cuando volví al muelle era muy tarde" (when I returned to the dock it was too late).