What is a group? A group is usually a collection of entities/items that have of similar characteristics or qualities. A simply analogy can be a WhatsApp group. Let's say you want to send an update about football game scores to three of your friends: Bob, Alice, and Tom. You would have to write and send the same message to each of the three people. If you create a WhatsApp group, name it Football Crew, and add Bob, Alice, and Tom as its members, it would be simpler to reference the single group because each member would receive the message.
A similar concept can be used on the ASA to reference multiple protocols, devices, or networks at a given time. This is known at an object group. Let's think about a scenario where we would like to apply one policy, whether to inspect, permit, or deny a group of different protocols, such as HTTP, Simple Network Management...