Limes, and not lemons, are the main citrus that gives the sharp sour and zesty flavour that Thai people so love. The larger, thick-skinned, yellow lemon is a temperate-climate citrus and does not grow in tropical Thailand. There is, however, confusion in the use of English terminology among Thai people, and limes are erroneously referred to as "lemons" in Thailand. (The Thai word for lime is manao.) Perhaps the reason is: the first westerners to translate local language into English did not know what limes were and called them lemons since they are sour like lemons. As a result, "lemon" has stuck and "lime" does not exist in Thai people's English vocabulary; therefore, in present-day recipe exchanges with English-speaking peoples, the mistaken term "lemon" may be used. Limes do have a much more intensely sour and zesty flavour than lemons, and although they may be substituted with the latter, the results definitely lack the vigor that limes give to Thai dishes. So use fresh limes whenever possible, but avoid the pre-squeezed or bottled varieties, which lack freshness of flavour.
Thai limes are smaller than American limes, but they are packed with flavour and juice. They are also a little sweeter and more similar to key limes. When using the larger American limes, I frequently need to add a little sugar to invigorate their flavour to approximate Thai limes. Because limes can vary in degree of sourness, as well as juiciness, the best thing to do when working with a recipe calling for lime juice is to go by taste. Often it is not the amount you use, as some juicy limes may lack the intensity of flavour that other dryer limes may possess. With cooked dishes, add lime juice toward the end of cooking since the fresh flavour of lime and its sourness can simmer away; exceptions are cooked dishes in which it is a background flavour.
In addition to the flavour it imparts, lime juice has a tenderising quality. Squid and rare meat, for instance, can become very tender and succulent from sitting in a lime sauce. Because of its tenderising capability, lime juice has been used as a common folk remedy to dislodge a fish bone accidentally stuck in the throat. If this should happen to you, try gargling with lime juice or sucking on a piece of lime, slowly swallowing the juice. It can soften the bone sufficiently in a short while, such that downing a mouthful of rice or water afterward can push the bone away.
Sources through East Asia: these varieties originate from the East & West of India, but are found throughout Micronesia, Thailand, Indonesia & The Malay Archipelago
Traditional Uses: Scurvy Preventative, vitamin C source, Acidifier in classic sour drinks, additive in fresh food and used as a seasoning
Exerted flavour profile: Acidifier, sourness, fresh fruit and body