Sense 1, somebody who is really loud and vocal.
Sense 2, somebody who lets out loud vocalizations, similar to the howl of a wolf, when they're in pain.

Beginning in the 1970s this was the popular term for a 'great party' in Western Canada. Its usage sprung from the enthusiastic party howls and hoots that could be heard at a distance from the many party-goers. It originated in North Delta (back when it was still unspoiled), a small, unique, adventurous, forested, geographically elevated suburban community bounded on four sides by the Fraser River, Burn's Bog, farmlands down to Boundary Bay, and the then sprawling, sparsely inhabited municipality of Surrey to the east. All ages of teenagers would end up partying together (most of them still friends decades later) on weekends in local forest clearings or in youngster's homes (when the parents went away on holidays!), and the loud, long howls of enjoyment we're the familiar signature of those memorable occasions. Those special celebrations of youthful freedom and friendship are still being enjoyed today. Rock on!

Someone who is disgusting and beyond the definition of ugly

Scientific name: Trollus Vulgaris Ulularis

An obscure subspecies of common troll, this lesser known internet denizen and lurker was brought back into the mainstream's view during the campaigns/elections for POTUS 2016.

With its characteristic scent of fear and ignorance, the howler repeatedly attempts to shout its personal truths into everybody else's reality using mostly blunt force internet tactics, relying heavily on logically fallacious ambushes and what it believes to be shiny objects.

Fueled by delusion and derision, convoluted arguments are constructed/fabricated and secured to each other by a near infinite number of tenuous threads at randomized intersections, maintaining many points of continuity with the original discussion while completely fragmenting coherency. Appearing on forums as vehemently vigorous to suffering extreme torpor and all points in between, the howler becomes tick-like and difficult to shake off once it has determined that you are prey and has attached its victim(s). Its rationales are unknown; it is uncertain if a howler can actually reason for itself, as none has ever observably demonstrated a fully intact brain or usable mind.

Usually, standard troll management techniques apply. However, at the time of this writing some have escaped off the internet and into public office; meatspace procedures are in the process of evolving to accommodate the contingency.

A sporting term used to describe a particularly terrible piece of play, usually due to the stupidity of a single player. A howler is not incurred through bad luck or even poor play, but rather through absolute amateurish hopelessness. A howler in soccer for example would be if a completely unmarked goalkeeper who was under no pressure inexplicably fumbled a simple ball into the path of an opponent who subsequently scored.

A derogatory term used in English denoting the ugliest person possible.

To have a particularly bad day, where nothing seems to be going the way it should.

Howler is often recognized as a magical item from the Harry Potter series, when in fact that is not all it is. In British slang, a 'Howler' is a boner. JK Rowling sure got all us Americans, didn't she?

When a football opinion is so phenomenally wrong that you feel the need to express yourself with the expression of “that’s a howler!”