something very cool, excellent
Que blusa pai d'égua essa que tu comprou!
What an awesome shirt you bought!
From the North and Northeast of Brazil, the expression joins pai (father) and égua (mare) to denote something of great value or quality — historically tied to breeding horses (the sire of the mare).
Falando's Idiom Trainer teaches you to recognize idiom meanings and create sentences using them, so you can speak like a Brazilian.