A classic Filipino dipping sauce consisting (literally, in the portmanteau sense) of soy sauce (toyu)and calamansi juice, though usually tarted up with the addition of minced labuyo chilli and garlic, onion or shallot.

Calamansi is a citrus fruit which grows in the Philippines and the Far East. You can substitute Asian Yuzu, which you won't be able to find either, or lime or lemon.
Labuyo are small triangular chillies quite similar to bird's eyes.