UTC is the modern reference standard
Coordinated Universal Time, abbreviated UTC, is the reference used to coordinate clocks worldwide. Applications, servers, aviation systems, and scientific work commonly store or exchange instants in UTC before presenting them in a user's local zone.
GMT is used as a time zone
Greenwich Mean Time is associated with the prime meridian at Greenwich. In everyday schedules, GMT means a zero offset from UTC. The United Kingdom uses GMT in winter, but switches to British Summer Time, UTC+1, during its daylight-saving period.
Do UTC and GMT show different clock times?
For normal conversion work, no. A timestamp at 12:00 UTC corresponds to 12:00 GMT. The distinction matters mainly when describing standards and regional civil-time rules rather than when reading the hour itself.
Which term should software use?
Use UTC for stored timestamps, APIs, logs, and technical documentation. Use a named IANA zone such as Europe/London when the intended local time must follow seasonal rules. A fixed label such as GMT cannot express the summer transition by itself.