An SNMPv3 group is a collection of users with similar access rights and privileges on a network device or system. In SNMPv3, access control is based on the concept of groups, and each group can have different access levels or restrictions. Members of a group can read or write various parameters, query particular SNMP objects, or perform specific operations on managed devices. SNMPv3 groups are a way to manage security and control access to network resources effectively.