small, very round citrus fruit that's ubiquitous in the Philippines; often used when green

also spelled calamansi

Scientific name:  Citrus microcarpa

Also known as: aldonisis, calamonding,  calamunding, Chinese orange, kalamondin, calamondin orange, Panama orange, kalamunding, kalamonding, kalamundin, calamundi

Kalamansi is a souring agent in the stews sinigang and paksiw. It is also spritzed on pansit noodles.

Mixed with soy sauce, it is a widely used dipping sauce and marinade. 

toyo't kalamansi
soy sauce and calamansi 

Watch Andrew Zimmern explain and show off kalamansi in his video on Filipino food.

Tagalog Workbook