A flotilla, or naval flotilla, is a formation of small warships that may be part of a larger fleet.
A Spanish flotilla being engaged by the Royal Navy in the action of 5 October 1804
A squadron, or naval squadron, is a significant group of warships which is nonetheless considered too small to be designated a fleet. A squadron is typically a part of a fleet. Between different navies there are no clear defining parameters to distinguish a squadron from a fleet, and the size and strength of a naval squadron varies greatly according to the country and time period. Groups of small warships, or small groups of major warships, might instead be designated flotillas by some navies according to their terminology. Since the size of a naval squadron varies greatly, the rank associated with command of a squadron also varies greatly.
A photo of Squadron in "keel line" : Squadron of battleships of the Germany class in keel line
The 2nd Battle Squadron of the Royal Navy's Grand Fleet during the First World War. From left to right: King George V, Thunderer, Monarch, and Conqueror.