Tapiada literally means 'walled up' or 'blocked off', often referring to a physical barrier. It's a less common word that evokes a strong visual.
In the song, Marc Anthony sings "Vieja mesa tapiada de amor" (Old table walled up with love). He uses tapiada metaphorically to suggest that the table is not just covered, but completely filled and overflowing with memories and emotions of love, almost as if those feelings have become an inseparable part of it.
Marc Anthony sings this one from across the room. He's at the bar while his ex sits at their old table with someone else: "Tú en la vieja mesa" ("You, at the old table"), "Tomando otro vino" ("drinking another wine"), "Con otra mirada" ("with another look in her eyes"). He stays "desde la barra" ("at the bar"), counting old affections one sip at a time, watching a stranger take his seat.
The chorus turns the table itself into the wound: "Vieja mesa tapiada de amor" ("Old table, boarded up with love"). It's not a metaphor he explains, just a piece of furniture he can't stop circling back to. He admits it outright, "la sigo esperando" ("I'm still waiting for her"), as if staying at the bar long enough might undo the whole scene.