From wikipidea:-

“Administrative Distance(AD) is a arbitrary numerical value assigned to a routing Protocol’”

A routing protocol with a lower administrative distance is considered "better" and is given priority over routing protocols with higher administrative distances.

Route Source Administrative distance
Directly Connected 0
Static 1
EIGRP summary route 5
External BGP 20
Internal EIGRP 90
IGRP 100
OSPF 110
IS-IS 115
RIP 120
External EIGRP 170
Internal BGP 200
Advertisements