To watch a large amount of a geeky television show, episode after episode, for a long period of time. A season of Buffy in two days, for example.

Similar to marathoning movies or chain smoking, but more geeky.
"I just mainlined the first 3 seasons of Angel"

"I'm going to go home and mainline the LOTR movies."

"Wheres Ferg at?"
"Oh, hes at home, sitting in the dark, mainlining Simpsons episodes"
by Anna Heavens January 27, 2009
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The act of binge-watching or binge-listening all episodes of a podcast or all episodes in a season of a TV show without breaking for sleep.
Mackey: Where were you last night?
Buddy: Aw, man, I was mainlining "Sense8." After the second episode, I was addicted!
by GypsyBowl July 5, 2015
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A person's main significant other, even though they may be dating several people at once.
"I got a lot of chicks, I ain't gotta lie. But you keep it real, so you my mainline." - Ray Vicks
by BRNOLA July 13, 2009
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the act of taking internet lingo and applying it to real life conversation

matt: I walked by a group of kids taking a test and said, "fucking scrubs."
joel: dude, you were totally mainlining.
by Taxt April 17, 2009
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A Canadian Youtuber who is known for his model train content and taking shots of maple syrup he is also allegedly a foamer
Did you see SMT Mainline’s video of that CP heritage Unit
by MinnesotaModelRailfan August 5, 2020
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Goes to country club, wears lululemon tennis skirts. Everything is Vineyard Vines and Monograms. Cadalak SUV and marries older rich husbands.
by Tomrocks February 25, 2018
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Doing heroin intravenously in the style of Robbie Williams. See also rock the mainline.
From Robbie Williams' "Rudebox":

"Ok then check the tan line
Make your body shape
Like you're stood on a landmine
Call me on my mobile
Not the landline
And jack the mainline
At the same time"
by Some Fresh Money September 8, 2007
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