This is the 2080th most frequent French word.
u
The letter "u" is the 21st letter of the French alphabet and represents a vowel sound.
Here, "où" ("where") acts as a relative pronoun introducing a relative clause giving more information about the museum.
Le musée où elle travaille est célèbre.
The museum where she works is famous.
The word "u" does not appear directly in this sentence; "s'il" is contracted for "si il". In English this is rendered as "if he" or "if it" depending on context. Here, "si" ("if") introduces a condition.
Je ne sais pas quoi faire s'il survient un problème.
I do not know what to do if a problem arises.
The word "u" is part of "où", which means "where" and is used to ask for location or position. It is pronounced /u/.