This is a Greece Small Hermes Head issue, a later print of the classic Hermes series produced between the late 1870s and 1890s. Printed in a vivid carmine-red, it shows the profile of Hermes, the messenger of the gods, framed by the traditional Greek meander pattern.
This 20 Lepta value is one of the scarcer mid-denominations of the series, especially in fine used condition with clear facial details. The example you provided shows genuine period cancellation, wide margins, and the typical coarse control characteristic of the later printings. These Small Hermes issues were printed typographically in Athens and remain an important part of Greek classical philately.