To be in the limelight is to be at the center of public attention. It might make you a little jealous if your best friend's acting career suddenly puts her in the limelight.
When a newly popular musician finds himself in the limelight, he might be surprised at all the attention. Someone who's in the limelight is constantly being talked about, interviewed, and photographed. In the early 1800's, theater stages were lit by heating a cylinder of the mineral called lime — the result was an intensely bright white light. The word limelight came to have its figurative meaning of "at the center of attention" in 1877.