GMT stands for Greenwich Mean Time. It is always UTC+0.
GMT is standard time. While daylight saving time is in effect, the same areas use BST (UTC+1) instead.
Right now London uses GMT.
Where GMT is used
Burkina Faso, Côte d’Ivoire, Gambia, Ghana, Guinea, Iceland, Ireland, Liberia, Mali, Mauritania, Senegal, Sierra Leone, Togo, United Kingdom.
In some of these countries GMT is used only in part of the country or only part of the year.