In mesh networking, APs have different roles.

MP: Mesh node that uses IEEE 802.11 MAC and PHY protocols for wireless communication. This node supports automatic topology discovery, automatic route discovery, and data packet forwarding. It can provide both mesh service and user access service1.

MPP: MP node that connects a WMN to MPs on other types of networks. This node can function as a portal for communication between internal mesh nodes and external networks1.

Neighbor MP: Neighboring MP with which an MP prepares to establish a mesh link1.

Candidate MP: AP that directly communicates with a mesh node2.

https://support.huawei.com/enterprise/en/doc/EDOC1100064365/90f2391e/configuration-examples-for-mesh  2: https://support.huawei.com/enterprise/en/doc/EDOC1100169459/8d79210e/configuring-wireless-mesh-networking