What is the meaning of various flags in the output of dig command?

Issue

• In the output of the dig command, I see the flags line. How to interpret those flags :-

[root@server ~]# dig example.com

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6 <<>> example.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 51834
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 2, ADDITIONAL: 2  =======> flags like qr aa rd ra etc. 

;; QUESTION SECTION:
;example.com.                   IN      A