San can mean a few things in Japanese, the most prominent (usually) are:
さん, san. San is used in combination with workplace nouns, such that a bookseller might be addressed or referred to as honya-san ("bookstore" + san), and a butcher as nikuya-san ("butcher shop" + san). San is sometimes used with company names. For example, the offices or shop of a company called Kojima Denki might be referred to as "Kojima Denki-san" by another nearby company. This may be seen on the small maps often used in phone books and business cards in Japan, where the names of surrounding companies are written using san. San can also be attached to the names of animals or even inanimate objects. For example, a pet rabbit might be called usagi-san, and fish used for cooking can be referred to as sakana-san. Both uses would be considered childish (akin to "Mr. Rabbit" in English) and would be avoided in formal speech.
三, san. The number three in Japanese.