Janice Hosenstein (later Litman, later Litman Goralnik), was Chandler Bing's on-again-off-again girlfriend on Friends. She is perhaps best known for her "nasal" voice and catchphrase: "Oh! My! God!" (years before the whole pausing between words thing was such a thing).
Her first appearance was in season one's The One With the East German Laundry Detergent, where Chandler and Phoebe decide to break up with their respective significant others. How Chandler and Janice met initially is never really stated, but they seem to find each other and reunite at random. As Janice said to Chandler during one of their break-ups, "something deep in your soul calls out to me like a foghorn: Ja-nice. Ja-nice." It's almost as if that's true. They keep falling back together. Yes, sometimes it's because Chandler gets lonely and calls her, but there have also been times it just sort of... happened. Like getting set up on a blind date, running into each other at a nail salon, or falling in love online.
Naturally, Janice is shown with Chandler the most, but does have some meaningful interaction with the other main characters. Although Janice is supposed to be a comic-relief style abrasive character, there is a wonderfully warm and caring side to her, as well. Examples of this include her discussion with Rachel right after both characters have given birth, and her comforting words to Chandler when she encounters him in a fertility clinic office.
I very much enjoy Janice's apprearances, and at one time, rooted for her and Chandler to end up together (pre-Mondler, obviously). They really grew together as people over the course of the show. Chandler encouraging Janice to reunite with her husband, even though he was deeply in love with her at that time, was a turning point. Yes, he ended the scene by changing his mind in an immature and comical fashion, but letting her go showed just how much he had grown up. Monica would have never ended up with Chandler if this shift in him hadn't taken place. In fact, Monica cited Chandler's immaturity as her main reason for not wanting to date him in the extended cut of The One With the Jellyfish.