A distress call is a signal from an individual or group requiring assistance or help to handle a situation spiraling out of control. The signal can be transmitted to a specific group known to be able to assist or generally.
Captain Lisa Cusak sent out a distress call after her escape pod crashed on a class L planet. However, due to the energy barrier surrounding the planet Cusak's signal was shifted three years into the future where it was picked up by the USS Defiant unbeknownst to both her and the crew of the Defiant. By the time the Defiant reached Cusak they discovered that she had been dead for years. (DS9: "The Sound of Her Voice")