Javu is the Manhattan restaurant at which Monica worked from "The One With The Male Nanny" (S9E06) until the end of the series. It is unknown if Monica kept working there after she and Chandler moved to their new house in Westchester, although she probably did.
While planning to move with Chandler to Tulsa in "The One With The Pediatrician" (S9E03), Monica made a phone call to a headhunter named Nancy and asked about chef jobs in that city but instead learned that Javu was interested in hiring her. Monica was thrilled with the news and immediately accepted the job. It is implied that Javu is a more prestigious and important restaurant than Monica's current employer Allesandro's; When explaining to Chandler her decision to remain in New York, she tells him that not even her career is more important that him but that taking the new job is something she has to do.
The job was seemingly a very positive experience for Monica. After her first day, she reported to Chandler "It's not just 'Health Department'-clean, it's 'Monica'-clean!". In The One With The Male Nanny Monica tells the friends that one of her new co-workers is "the funniest man" she's ever met, prompting so much jealousy from Chandler that Monica eventually invents a story about an offensive joke to reassure Chandler she no longer finds the man funny.
Upon learning that Javu is so popular that diners must line-up outside, Phoebe decides to relocate her guitar-playing to entertain those patrons in The One With Rachel's Dream. Monica doesn't feel that Phoebe's music is suitable for the atmosphere of the restaurant and a feud develops between the two that culminates with Monica and Phoebe polling the restaurant full of diners about their tastes. The friends eventually end their fight, but not before Phoebe calls Monica's cooking "Pretentious-comma-garlicky."