A 250mA slow-blow fuse is an electrical safety device designed to protect circuits and electrical equipment from overcurrent conditions. The "250mA" indicates its current rating, which is 250 milliamperes or 0.25 amperes. Unlike fast-blow fuses that respond immediately to overcurrent’s, slow-blow fuses have a delayed response, allowing them to tolerate temporary surges in current while still providing protection against sustained overloads.

These fuses are often used in applications where precision and time delay are crucial. When an overcurrent condition occurs, the fuse's delayed response allows it to withstand short-lived current spikes that might be typical during normal operation. However, if the overcurrent situation becomes sustained and potentially damaging, the fuse will eventually blow to interrupt the circuit and prevent damage to the electrical system and connected devices.