Hey Guardian. You won't find a specific description of what a "casual gamer" or a "casual player" is and probably you will receive different opinions based on different criteria depending to who you're asking this question. For example, my personal view of a casual gamer/player could be completely different to that of a streamer. Generically speaking, casual players on D2 are those that experience the game enjoing the most basic Contents on every aspect offered by the game. A Casual Player may log in every week, complete Banshee, Vanguard, Crucible and Gambit Challanges for Pinnacles and Bright Dust or they may decide to avoid one of them because they don't like it, for example don't play Gambit or Crucible. Casual players usually are not into things such as META or Builds. They use Equip and Subclass they feel more comfortable with or what they enjoy the most despite theyr efficiency in the situation. A Casual Player, for example, might jump into the Crucible with Weapons and Armor Mods that are useless or not optimal for PvP. Casual players tend to avoid End Game contents such as GM Nightfall, Raids or Trials for a reason or another. It may be because they find them too hard, don't have enough time to prepare for them, or because they have no one to play with ecc. On the other hand Casual Players are very active in Seasonal Contents, they usually grind Challanges and Triumphs for Titles and other rewards. For a casual player also a Master Lost Sector could be a challange. That's pretty much it. But again, remember that this is a very generic view.