perihelion -- noun. This is the point (or moment) in Earth's orbit when the we are closest to the Sun. Johannes Kepler realized that our orbit isn't circular, but elliptical instead. It's only slightly elliptical, so in the grand scheme of things, the difference between perhelion and its opposite, aphelion (when we are farthest from the Sun), is rather small: only some 5.1 million kilometers.
Distance from the Sun doesn't really have much to do with the seasons, contrary to what you might assume. In fact, perihelion occurs around January 4, and aphelion occurs around July 4.
The Wikipedia informs me that perihelion is a more specific term for the general idea of periapsis. That's probably more than even I wanted to know.