Uncertain. Possibly from Gothic *𐍀𐌰𐍂𐍂𐌰 (*parra), *𐍀𐌰𐍂𐍂𐌰𐌽𐍃 (*parrans, “trellis; fencing”) or from a pre-Indo-European root of similar meaning.
Practice speaking and memorizing "parra" and many other words and sentences in Catalan.