a navy officer of the highest rank who is in command of the entire fleet of warships, equivalent to the general or field marshal of the army;
(in some countries) the supreme commander of a fleet of warships, who is above the rank of a vice admiral and below the rank of a fleet admiral;
(in British usage) the master (commander) of a fleet of fishing boats (nothing to do with the Navy or warships),
After retiring from the Navy, he was appointed as an admiral of a fleet of fishing boats.
There are more female admirals in the Navy now than there were some years ago.
It is to be noted that in peace time there are four different kinds of admiral ranks: four star admiral; three star admiral; two star admiral (or upper half); one star admiral (or lower half).
Note: ‘Admiral’ is also used to refer to a kind of butterfly, white admiral or red admiral, which looks very attractive with red and black patterns on its wings.