Eccentricity describes the shape of the Earth’s orbit.
It ranges from the orbit being almost a perfect circle to being an oval, and returns to nearly circular shape. It takes 100,000 years for the orbit to accomplish such cycle.
In winter the orbit is nearly circular with Earth being a bit closer to the Sun in January than in July. Therefore, at this point in time, the orbit’s eccentricity has very little effect on the planet’s climate during a year. However, if the orbit was a pronounced oval, eccentricity would be a dominant factor affecting the climate, with Earth being warmer when it was closer to the Sun. The difference between the seasons would also be more pronounced.