BGP aggregate-address
The aggregate-address command creates an aggregate entry in the BGP table. This aggregate entry can then be advertised to other BGP routers. However, this command cannot be used to initially advertise networks. It will only aggregate prefixes that are already in the BGP table. In order for these prefixes to be in the BGP table initially, they must fulfil certain prerequisites.
The aggregate feature is described in the RFC as a transitive attribute.
Links
https://datatracker.ietf.org/doc/html/rfc4271#page-30
https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/5441-aggregation.html