AdvanceShipping (also known as Ash/May, AaMayL, and SatoHaru) is the belief that Ash Ketchum and May, two of the protagonists of the Pokemon franchise, are or will be romantically involved. The ship is supported by both VineShipping and HydroShipping.
Over the anime with May as main protagonist, she had caught similar or identical Pokemon to Ash. Both trainers have a Bulbasaur (VineShipping) and a Squirtle (HydroShipping). May has a Munchlax, while Ash a Snorlax. Also, they both have fully-evolved fire-starter types (Charizard and Blaziken, respectively), as well as bug/flying (Butterfree and Beautifly).
Throughout the course of the anime, there have been several "rival" ships, few of which have a reasonable amount of hints. The ships that tend to be the biggest threat to AdvanceShipping are PokeShipping and ContestShipping, and to a lesser extent, PearlShipping. However, PokeShipping is now less of a threat because Misty has been running her gym since before May left the group.