In audio, “bleed” is the leakage of one audio source’s output into another audio source’s input. This can happen onstage, such as drum or cymbal sound bleeding into a guitar amp mic, or in the studio, such as the output from a singer’s headphones leaking into the vocal mic.
Some solutions to reduce bleed include: mic selection and placement — using a cardioid or supercardioid mic on a source to reject signals from other directions; using noise gates to attenuate mic sensitivity to prevent pick up of outside noise; and optimizing the gain stage of your mixer and peripherals to achieve an ideal signal-to-noise level.