Exhibitors, exos, are movie theaters and any outlet that pays to screen a film or event. Distributors, distros, are anyone that owns the right to sell a property; movie studios, license holders, etc. Offerings are any products to air or are sold, packaged.
Distributors sell their products to exhibitors. Exhibitors have limited space, time, and most important of all premium screens. By announcing ahead, other distros are aware of how to program (release product to exos).
For example, WBD wouldn't release Dune Part 2 on the same weekend as November 10th. It would burn Exos who only have so many PO/PS/PXs (Premium offerings/screens/experiences) to offer. So an Exo would have to choose, "Am I showing The Marvels or Dune part 2 on my 2 IMAX screens this weekend?"
Dune Part 2 releases the week before the Marvels for that very reason. Generally, there is a working agreement to not program counter another franchise. It's why films are released as they are.
The US opening box office is immensely important to the business.