Multicast ip pim rp-address override
When implementing PIM sparse mode in a multicast topology, the ip pim rp-address command is used to statically configure the address of the RP. However, it is possible to dynamically configure an RP. This can be done using various discovery protocols, such as Auto-RP and PIMv2 Bootstrap (BSR).
If you have configured both a static RP on the local router, but dynamic RP discovery is also configured, then by default, the dynamically learned RP will take precedence over any statically configured RP.
Now the override keyword used in this command specifies that the statically configured RP will take precedence over any dynamically learned RP.
Links:
https://networklessons.com/multicast/multicast-ip-pim-auto-rp
https://networklessons.com/multicast/multicast-pim-bootstrap-bsr