This command is used to find the hostname or IP address of the server where it is resolving. Below are the example for your reference -
ping -a 123.*.*.* -----> When you will fire this command then it will return the output as hostname in below format -
Pinging hostname [123.*.*.*] with 32 bytes of data:
Reply from 123.*.*.*: bytes=32 time
Hope this will clear your idea.