I just spent a few minutes working this out…
if we have 10.0.0.0/24, 10.0.1.0/24, 10.0.2.0/24, 10.0.3.0 /24 networks and we aggregate it with:
aggregate-address 10.0.0.0 255.255.248.0 suppress-map ciscomap
route-map cisco deny 10
match ip address prefix myprefix
ip prefix-list 10.0.3.0/24
… then 10.0.3.0 will NOT be suppressed.
suppress-map means suppress these networks that are defined by the route-map. The deny statement in the route-map means do not include these networks in the suppress map that be default suppresses everything if we had only permit statements in the route map.