A personal WiFi router is generally used for residential purposes. They are directly connected to a modem that is provided to you by your Internet Service Provider (ISP) and are capable of propagating wireless signal throughout a home.
Rogue Access Points (APs) can be set up innocently or with malicious intent. They can cause interference with your WiFi network, present vulnerabilities to security, and have devices on your network connect to it instead. Whether it's a part of WiFi Health Checks or security analysis and monitoring, it's always a good idea to know how to physically locate these rogue Access Points.