PHILADELPHIA – It’s called “25 Random Things About Me.” It lives on Facebook, the popular social-networking Web site. It’s a list you fill with 25 items of personal information, ranging from the trivial to the intimate.

Trivial: “I hate tuna.” Personal: “Part of me hasn’t grown past the moment of my father’s death.” Intimate: “I have been unfaithful, but so far it hasn’t mattered much.”

You send your “25 Random Things” chain-letter-style to 25 friends, and they fill it out and tag 25 others, and …

And soon Facebook – a virtual living room where people hang out and tell everyone else what they’re doing and thinking – is awash with personal revelations, admissions, info once kept private.

Facebook turned 5 Feb. 4. Sometime in mid-January, “25 Random Things” became a wildfire fad there.

Many have called Web lists such as “25 Random Things” “narcissism,” a word that means egocentrism, with its not-so-great overtones. But Facebook users and experts are saying: Not so fast. Of course, ego is involved. But “25 Random Things” is a product of the information age. And that age is simply different from what went before.

If they are right, “25 Random Things” reveals a decisive shift in our society, and there’s no going back. Many of us – younger, mostly – take a distinctive view of private and public, in which a permanent, always-connected audience trades personal, even intimate, information as part of having friends and being social. That hyperconnected life is here to stay. Call this narcissism, but it might be that the train left and you weren’t on it.

Facebook spokespeople say that they do not keep statistics on members’ activity, but that membership, and the use of “Notes” (where “25 Random Things” lives), spiked last month.

Emily Nussbaum, editor-at-large for New York magazine, says the most decisive difference is that the Facebook generation “assumes they have an audience”: They have a mental image of a large group of people interested in postings such as “25 Random Things.” Part of their identity rests on an invisible entourage that accompanies them everywhere.

The members of the Facebook generation are right. They do have audiences. This is how they were socialized.

Young people are hardly the only ones with that invisible entourage. The businessman furiously inputting on his BlackBerry; that lady serial-cell-phoning on the train – all are connecting with a world of others there in all but body.

That communal aspect is what so much commentary misses about “25 Random Things.” It’s not just a list; it’s a communal exercise. Posters post, and friends comment.

What’s that commentary like? An unscientific survey of more than 30 such lists has yet to uncover anything vicious or unkind. Mostly, the virtual community is, in Nussbaum’s words, “surprisingly supportive, sweet, even encouraging.” It is nurturing, a thing friends do.

Nussbaum says the social-networking generation has come to expect this trade in personal details: “It comes with having a circle of friends.” Older users – who have joined in increasing numbers the past two years – initially may find it unnerving, but in time, most adjust to the culture.

Clive Thompson, contributing editor to the New York Times Sunday Magazine and columnist for Wired, says society is “redrawing the boundary between public and private, and in some respects, it’s the most significant intergenerational cultural shift since rock’n’roll. People separated by only five years of age are looking at each other, completely baffled by their behavior.”

There are certainly downsides. Christine Rosen of the New Atlantis, writing by e-mail, reminds us that narcissism is narcissism: “For all of their apparently casual tone, these lists are not filled with random things. They are carefully and deliberately crafted efforts to market their makers as quirky and appealing people. The revelation of one person’s quirks can be endearing, but the broadcasting of hundreds of thousands of people’s quirks quickly devolves into tedious mass solipsism.”