Most Call of Duty online multiplayer but games have both single-player and multiplayer modes. Single-player mode typically features a story-driven campaign with missions to complete, while multiplayer mode allows players to compete against each other online.
In multiplayer, players can engage in various game modes, such as team deathmatch, capture the flag, and battle royale. Multiplayer also includes a leveling system and a wide range of weapons and equipment to unlock as players progress.
That being said, there have been some Call of Duty games that have not included a single-player campaign and were focused solely on multiplayer, such as Call of Duty: Black Ops 4.
In conclusion, while Call of Duty is primarily known for its online multiplayer experience, it varies from game to game and some titles offer both single-player and multiplayer modes.