R and S are letters in the English alphabet, where R is the 18th letter and S is the 19th. They are both consonants and are commonly used in various words. The letter R is often associated with sounds made by vibrating the tongue against the roof of the mouth, while S produces a hissing sound. In terms of phonetics, R can represent different sounds depending on the language, such as the American English "r" or the Spanish rolled "r." The letter S is frequently used in plural forms and can also represent the voiceless sibilant sound. Together, R and S contribute to the richness of language and communication.