Fans of the photo-sharing Web site Flickr often use two words to describe it.

Addictive, for it is. And phenomenon, ditto.

A startup now owned by Yahoo, Flickr isn’t just another online place to store your photos and have prints made. Flickr is about sharing your photos with the world, and in the course of doing so, concocting countless ways to have fun with them, whether by organizing them with tags (like “soccer” or “vacation”) or reveling in the creativity of other shutterbugs.

With Flickr, your uploaded images become a part of your personal “photostream.”

You can then classify them as public or private, organize them into collections (called “sets”), or join specialized groups for sharing photos, with names such as Sunflowers (photos of just that, with 120 members) and City Sunsets (1,009 members). With your permission, other people can tag your photos and comment on them.

These Flickr features make photography a social and serendipitous activity, rather than a solitary one, essentially creating the thriving, always-evolving subculture that is Flickr.

To get a quick sense of this, just consider a feature at Flickr known as geotagging. With geotagging, you can “tag” photos with a specific geographic location, down to the precise longitude and latitude.

This not only allows you to keep track of where you snapped your own photos, but also lets you explore photos from other places around the world (or, literally, your own back yard, or your neighbor’s).

Within 24 hours of Flickr’s introduction of geotagging, more than 1.2 million photos had been tagged with their locations.

Flickr also lets others with technical know-how tap into its wizardry. Flickr is constantly spawning other spots making creative use of Flickr’s innovations. In the case of geotagging, there is something called Trippermap (www.trippermap.com), where you can create a personal, interactive map of your Flickr photos for use on your site or blog.

All of this may seem like sensory overload. And, to be sure, an initial visit to Flickr may have you running for the hills, thinking you just want to snap your photos, get prints and maybe let your in-laws see the baby.

Don’t run so fast.

Once you get the hang of things, Flickr will woo you gradually, letting you test out its nifty features and bounty of add-ons and tools. It is the latter – the extras from both Flickr and others – that really make Flickr what it is.

These will help you create Flickr screensavers and even play games involving Flickr tags and images.

I could go on and on about Flickr extras, but that would fill a book.

In fact, it has. “Flickr Hacks” (O’Reilly, $24.99) delves into all of the useful and out-there ways you can employ Flickr.

For more tips, go to www.quickonlinetips.com and click on “Great Flickr Tools”; or www.flagrantdisregard.com/flickr/; or www.flickrnation.com.

Flickr is free, but free accounts are limited to uploading 20 megabytes worth of photos each month. A pro account, for $24.95 a year, ups the limit to two gigabytes and gives you permanent archiving of high-resolution images.