The term direct rays can be used with reference to sunlight or rays of light originating from the Sun and hitting the Earth.
Rays of light from the Sun strike the surface of the Earth at different angles. Those that are perpendicular to the surface of the Earth are known as direct rays. The other rays are referred to as indirect rays.
Direct rays strike the Earth at the equator throughout the year. As the Earth moves around the Sun the inclination of the axis relative to the Sun changes. This results in different seasons. An interesting point to note is that when summer and winter occur is not dependent on the distance of the Earth from the Sun, rather it is more to do with which areas are getting hit by relatively direct rays of sunlight.