On Radix, shard groups [ /ʃɑrd grups/ ] are sets of validators that are responsible for storing and validating the ledger state on subsets of the Radix shardspace. Unlike the shardspace itself, which is fixed at 2^256 shards, shard groups are dynamic and can adjust their shard coverage according to demand.
In a decentralized network, data is distributed across multiple nodes to improve scalability and resilience. Shard groups are a way of organizing these nodes and data in a structured and efficient way. Each shard group is responsible for a subset of the network's data, and the nodes in the shard group work together to process and store this data. The data in a shard group is typically related in some way, such as being part of the same transaction or coming from the same geographic region. This allows the nodes in the shard group to efficiently process and store the data, and to quickly respond to requests for the data.