Soi is a term used in Thailand to refer to a side street branching off a major street. It is commonly used in Bangkok, where sois are usually numbered and referred to by the name of the major street and the number, such as "Soi Sukhumvit 4" or "Sukhumvit Soi 4". When walking on the major street towards increasing soi numbers, all the even-numbered sois are on the right side and the odd-numbered ones on the left side of the street. Sois can also have names, often named after important landowners or families of landowners who had land in the area in the past.
Additionally, "soi" is used in speech, often in an ironic way to say that one knows about something because it is easy to see it just by looking. Furthermore, "SOI" can also refer to "Silicon on insulator" technology in semiconductor manufacturing, which involves the fabrication of silicon semiconductor devices in a layered silicon–insulator–silicon substrate to reduce parasitic capacitance within the device, thereby improving performance.
Finally, "SOI" can also stand for "Southern Oscillation Index," which is a standardized index based on the observed sea level pressure differences between Tahiti and Darwin, Australia, used in the study of El Niño/Southern Oscillation (ENSO) .
