Which optional feature is available for some endpoints to enable multiparty calls to be hosted directly on the local endpoint?

Ad hoc refers to unscheduled call creation, not to the capability of hosting a multiparty conference on the endpoint itself.

Webex-enabled Cisco TelePresence describes cloud registration of endpoints to Webex, not a local multiparty hosting feature.

Multiway is a feature that escalates a point-to-point call to a multiparty conference by invoking an external conferencing bridge, not hosting locally.

Multisite is an optional license available on select Cisco TelePresence endpoints (such as the MX and SX series) that activates an embedded conferencing capability. It allows the endpoint to act as its own bridge, hosting multiparty calls locally rather than relying on an external infrastructure component like a TelePresence Server or Conductor.

MeetMe is a CUCM conferencing feature for scheduled dial-in conferences, not a capability hosted directly on a room endpoint.