It generally refers to three activities:

• No. 1: The unveiling of new television network schedules
• No. 2: The cajoling of advertisers by the networks
• No. 3: The selling of billions of dollars in advertising time
  
  
  "The (TV network) presentations (to advertisers) are really only the start of the upfront process. Typically, after the networks make their presentations, the sales executives take over, beginning negotiations with (ad) agencies, who are bargaining on behalf of marketers, about buying commercial time in advance for the coming season. (That is how “upfront” gets its name, as the dealing happens ahead of time.)"
  
  
  2012 Upfront News & Resources
   

  Ad Age	Ad Week	B & C	Hollywood Reporter
  TV Nets At Upfront Pitch Shows' Social-Media Traction The Buzz Behind the Scenes at Upfronts Ad Age's Annual Upfront Picks and Pans Univision Upfront Opens With Sofia and Closes With Shakira Think Web Video Can Challenge Upfronts and TV? Fuhgeddaboudit! Ad Age's Cheat Sheet for the Broadcast Upfronts	CBS Upfront: Sales Pitch or Victory Lap? The 10 Best Upfront Presentations (So Far)	Upfronts 2012: CBS Affiliates Believe New Slate Will Keep Them on Top Upfronts 2012: CW Shifts Six of Its Seven Returning Series Upfronts 2012: ABC Affiliates Want Improvement From Net	STORY: Upfronts 2012: Complete Network Scorecard Fall TV 2012: The Full Schedule

  
   

  New York Times	Reuters	TV Week	WSJ
  At Network TV’s Gathering, Web Is Central The Upfronts en Español A DVR Ad-Eraser Causes Tremors at TV Upfronts CW Network Unveils a Remake of Its Schedule Comedies Lead the Way for the Next TV Season Pursuing Advertisers With Big-Top Spectacle	TV networks aim to laugh to the bank at "upfronts" CBS beats Street on advertising, Web video	CW's Fall Schedule Bets on Classic Characters, Shifts Network Staples Into New Slots CBS Unveils Fall Schedule, Adds Four New Series to Lineup ABC's Fall Lineup Unveiled, as the Network Bets Heavily on Its Current Freshman Crop; Here's the Full Schedule	Video: A Guide to the New Fall TV Shows ABC Unveils New Fall Dramas

  
  
  2011 Upfront News
   

  Advertising Age	Ad Week	B & C	Hollywood Reporter	New York Times	Reuters	TV Week	WSJ
  CBS Opening Bid for Upfront: Up 18% TV Upfront headed toward double digit gains Where to Tune in for Upfront Week's Biggest Events Who's Who Among TV's Top Wheeler-Dealers   TV Land Joins Ranks of Big Broadcast at Upfront Thanks to 'Hot' Sitcoms Why All This TV Upfront Excitement Needs a Grain of Salt	The Programming Insider: CBS Finales Best ABC CBS Changes Every Night of the Week The Programming Insider: The Upfronts, Day Two	Upfronts 2011: Univision Offers Unique Take on ‘Biggest Loser' Upfronts 2011: CW Adds Four New Series to Fall Primetime Schedule CBS Unveils Primetime Schedule With Five New Shows in Fall Glitches Zap Turner Upfront Discovery en Espanol to Add 50 New Series for 2011-12 Affiliates Guardedly Optimistic About NBC Upfront Presentation	2011 Complete Coverage	Best and Worst Scenes From Upfront Week Networks Try a Social Media Spin at the Upfronts Upfronts: Turner Brings New Series to TBS and TNT Upfronts: Discovery Ups the Stakes in Hispanic Media Upfronts: CBS Adds Three Dramas, Two Sitcoms for Fall TV Steps Up Pitch to Hispanic Market For Fox and NBC, Let the Singing Begin After Weak Season, Networks Strive for Fresh Idea	ABC looks to the past with TV lineup, orders 13 shows Fox banks on dinosaurs, Simon Cowell in new TV lineup	CBS Unveils Primetime Schedule With Five New Shows in Fall ABC Overhauls Lineup for Fall--Eight New Dramas and Five New Comedies on Tap CW Announces Drama Pickups; Sarah Michelle Gellar in the Mix	CBS Updates Its Take on Drama CBS to Move 'CSI' as Network Updates Crime Show Formula TV Smiles Kindly on Comedies

from 2010

Meantime, all of the networks are purchasing newspaper ad space to tout their new lineups.

See these full-page newspaper ads from FOX , NBC and TBS/TNT (May 17) and this ad for ABC  (May 18)
A&E Network ad (AdWeek)