1. A type of warship - intended to be somewhat smaller than a battleship but faster and more maneuverable (relatively). They were designed to act as a recce element, scouting ahead and perhaps luring the enemy onto the slower moving main fleet of battleships who were more heavily armed.
Both fleets at Jutland operated cruiser screens, neither with any great success.
Cruisers have also spawned many variants such as Light cruisers & Heavy cruisers (self-explanatory), Battlecruisers (a half-way house between cruiser and battleship, with a huge overlap into battleship) and others such as "Pocket Battleships" aka Panzershiffe which were fast medium cruisers with full-sized battleship guns, but only a limited number.
Cruisers are the biggest big-gun warships currently used by the navies of the world after aircraft carriers showed battleships to be far too vulnerable to air attack. Cruisers are barely any less vulnerable, but are less expensive and politically damaging to lose.
The last "real" cruisers that the Royal Navy possessed were the "Tiger"-class, HMS Tiger, Lion and Blake, with the last decommissioning in 1979. However, as a sleight of hand, the British Invincible class mini-carriers were put-through the procurement process as "through-deck cruisers" to allay any suspicion on the part of the SoS1 that Britain was going to have any more of those expensive, imperialist aircraft carrier things.
2. An inter-war/WW2 tank classification used by the British to describe a fast moving, lightly armoured, maneuverable tank with a good anti-tank gun2 intended to act as a modern equivalent of cavalry. The alternative being the Infantry tank, slow, very well armoured, with a smallish gun, intended to support infantry assaults.
The Cruiser/Infantry tank concepts became obsolete after WW2 with the invention of the Main Battle Tank in the form of the Centurion etc. that could do both jobs so well that there wasn't a lot of point having separate classes.
3. A gentleman who cruises the parks and commons of England in search of sexual excitement.
1Denis Healey. Who'd just canned the Ark Royal replacement.
2Or at least, a good anti-tank gun until they met a Tiger.