People of a certain age were trained to use exclamation points to indicate excitement or even anger. And they never imagined that a simple period at the end of a sentence could get them into hot water.

But the social-media age has twisted the meanings of some of our most basic words and punctuation marks, reveals Wired magazine’s resident linguist Gretchen McCulloch in her new book, “Because Internet: Understanding the New Rules of Language” (Riverhead), out July 23.

In our current world, periods are now seen as aggressive, and a cartoon of a smelly poo is considered perfectly acceptable communication.

While some might feel baffled by these new forms of internet expression, McCulloch thinks they’re “fantastic.”

“I’d gladly accept the decline of standards that were arbitrary and elitist in the first place,” she writes, “in favor of being able to better connect with my fellow human beings.”

Here are a few of the ways social media has changed the meaning of words, created new ones or even altered society’s perception of our most basic punctuation marks.

‘KEYSMASH’

Definition: The “haphazard mashing of fingers against the keyboard to signal a feeling so intense you can’t possibly type real words.”

So, if someone types “asdfkf;jas” in a tweet, they’re likely trying to say they’re overwhelmed.

McCulloch notes that the keysmash, despite its chaotic appearance, follows repeatable patterns.

Lines of keysmash “almost always begin with the letter ‘a’ and often begin with ‘asdf,’” McCulloch writes. They usually then contain the letters g, h, j, k, and l plus a semicolon — the middle row of the keyboard — in random order.

This indicates that people who use keysmash are usually touch typists, since the “frequently occurring characters are the home row of keys [with fingers in] the rest position.”

But also, random characters are not as random as they appear. Based on an “informal survey” of keysmash enthusiasts, McCulloch learned that “the majority of people will delete and remash if they don’t like what it looks like.”

The ‘hostile’ period

Using a period for short messages has come to be seen as outright aggressive by Gen Z.

The first widespread indicator, McCulloch writes, came in 2009, when an Urban Dictionary user defined a period as “the new cool way to emphasize (usually moody-ass) sarcasm.”

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For example, read these two sentences below and try not to feel a tiny bit slighted by the second version:

Really, you’re doing great!

Really, you’re doing great.

By 2013, the “hostile” period had been covered by New York magazine and The New Republic.

This new approach to the period makes sense when you consider punctuation as “a marker of typographical tone of voice,” McCulloch writes.

“Just as a question mark can indicate rising intonation, the period can indicate a falling intonation,” she writes, adding that the period lends a feeling of solemnity to a statement. “In ordinary conversation, we don’t speak in full sentences, and we especially don’t round them all off with a distinct fall.”

Exclamation points!!!

In internet speak, exclamation points indicate enthusiasm. Conversely, not using them can make you sound like a heartless shrew.

“The exclamation mark is frequently repurposed to indicate warmth or sincerity, rather than just excitement,” McCulloch writes. “A 2006 study found that in e-mails, exclamation marks were used to indicate excitement only 9.5 percent of the time.” By comparison, they indicate “friendliness 32 percent of the time.”

The marks have come to be seen as so indicative of warm online communication that McCulloch recommends people install “Emotional Labor, a Gmail add-on that promises to ‘brighten up the tone of any email!’ — largely by adding exclamation marks at the end of every sentence.”

Ellipses …

While older folks may use ellipses to indicate a line separation, these three little dots, like the “hostile” period, have come to mean more to the younger generation. “For internet-oriented writers, the dot dot dot . . . [has taken on] a meaning of something left unsaid,” McCulloch writes. “When dealing with the generations above them, the [younger cohort] often over-interpret: They infer emotional meaning from minor cues that are more subtle than the older folks ever dreamed of sending.”

Poo emoji

Given its crudeness, the poo emoji, inspired by a 1980s Japanese comic, almost never made its way to our keyboards.

In 2007, Google decided to adapt emoji to Gmail — partly to attract more users in Asia, where the characters are widely used. But Google’s head office at first wasn’t convinced that the poo symbol was appropriate.

“The Japanese engineers had to explain its importance to the home office,” McCulloch writes. Rather than simply being rude or offensive, the engineers told their bosses, a poo emoji generally means “I don’t like that — but softly” or “That’s unfortunate, and . . . I am displeased at what has just been expressed,” McCulloch writes. “It’s the anti-like.”

LOL

While some older folks have long mistaken LOL for the phrase “lots of love,” McCulloch notes that the “laughing out loud” abbreviation is not as straightforward as people think.

“While ‘lol’ started out indicating laughter, it quickly became . . . a way of appreciating a joke or defusing a slightly awkward situation even if you didn’t technically laugh at it,” McCulloch writes.

“As early as 2001, the linguist David Crystal was doubting how many lols were truly ‘out loud,’ and as one widely shared Reddit post put it, ‘We should change ‘lol’ to ‘ne’ (nose exhale) because that’s all we really do when we see something funny online.”

An informal survey McCulloch conducted in 2017 found that younger people reject the literal meaning outright and instead prefer the LOL “meanings of amusement, irony and even passive-aggression.”