the.com/perihelion

the moment Earth snuggles closest to the sun, smack in the dead of winter

means The point in an orbit where a planet, comet, or other body swings closest to the Sun.

from From the Greek 'peri' (around, near) joined to 'helios' (the Sun) — the same 'helios' that lights up helium and heliotrope. The pairing was coined by astronomers in the 17th century, modeled on the older Greek-flavored vocabulary of the heavens, to name the near point of an orbit; its mirror twin, 'aphelion,' uses 'apo' (away from) for the far swing.

January thing: Earth reaches it in early January, hemispheres be damned
Not the reason: Seasons come from tilt, not this 3-million-mile swing
Speed boost: Planets move fastest at perihelion, slowest at aphelion
Mercury's tattle: Its shifting perihelion helped prove Einstein right
Name roots: Greek for around-the-sun, coined by Kepler era

for instance

earth perihelion — occurs around january 3 each year, ~147.1 million km from sun

mercury perihelion — closest planet to sun at ~46 million km, causes relativistic orbit precession

halley's comet perihelion — last occurred in 1986, next in 2061, comes within 54.3 million km