There's some pretty good definitions on the FAQ page.

The world of alpines is huge and most are cold hardy - they do, after all, grow and thrive in alpine regions. It's getting the conditions they like to grow in that is the trick.

Here is a link that might be useful: FAQ

A strict definition of alpine plants is "plants that grow in the Alps". However, "alpine" is also used to describe other mountainous areas of the world that are above timberline. Some of the "alpine" species found in those mountainous regions are also found in the Arctic tundra.

Alpine plants are always cold-hardy but there may be other climatic conditions particular to your area that may make it difficult for certain alpine species to thrive or even survive. The first and most important is the characteristcs of your summers.

Most alpines do not enjoy high temperatures and high humidity. I live at 10,000 feet in the subalpine zone of Colorado. I can grow hundreds of alpine species from all over the world because I have sunny but cool summers. If you live where your summers are hot and humid or if you get rain or ice in the winter, you may want to considered growing alpine species in a controlled environment, such as an alpine house.

Many times "alpines" are lumped together with the more vague term "rock garden" when describing low-growing species. Combining "alpine" with "rock garden" species allows gardeners in the southern part of America to enjoy a simulated "alpline" environment.

I have about 1,000 species of cold-hardy, low-growing species at Mountain View Experimental Gardens. You might be interested in the link below which will take you to descriptive photos and propagating and growing specifications for many of those species.

Some very common ground covers can be incorporated into a natural or contrived rock garden, such as Maiden Pink (Dianthus deltoides), Snow-in-Summer (Cerastium tomentosum), Creeping Veronica (Veronica repens), Rock Soapwort (Saponaria ocymoides), Purple Rockcress (Aubrieta deltoidea), Creeping Phlox (Phlox subulata).

Some ground covers can become very aggressive but you can "nip this in the bud" by planting them in very infertile soil made up of a good portion of coarse sand and pea-size or smaller gravel.

After you have a small population of unchallenging, reliable-flowering, rock-draping ground covers, you can then begin to seek out taller species (up to about 10 inches). Many true alpine species have very large flowers on very short plants. They don't have a lot of time to attract pollinators before the cold weather returns so they "advertise" their flowers like neon signs.

Some tall, well-known garden plants may have a cultivated dwarf variety. For instance, Iceland Poppy (Papaver nudicaule) usually grows from 18 to 24 inches tall. It has very large, showy flowers and it is a continuous bloomer throughout my "green" season. It's too tall for a rock garden but it has two short cultivated varieties (cultivars): 'Garden Gnome' and 'Wonderland'. These two cultivars are between 8 and 10 inches tall and still have large, showy flowers and the same long bloom time as the tall version.

Shasta Daisy (Leucanthemum maximum) has a dwarf cultivar of about 10-12 inches tall. Even those tall, stately Foxgloves (Digitalis purpurea) have short relatives, such as Perennial Yellow Foxglove (Digitalis grandiflora) at 12-18 inches tall. Columbines are everyone's favorite flower in Colorado. The usual height is between 20 and 30 inches. But the cultivar 'Dwarf Fantasy" stands only 5 inches tall and the red & white 'Danish Dwarf' is just 8 inches tall.

Some low-growing high-desert species may also work for you. Google "Plants of the Southwest" or "High Country Gardens," both in New Mexico, to get some ideas. Also, for alpine species, take a look at "Rocky Mountain Rare Plants" (rmrp.com) and "Alplains" (alplains.com) in Colorado.

I hope this helps you decide on species for your garden.

Here is a link that might be useful: Mountain View Experimental Gardens

Thanks for the description from janeh, CO. The only question is on the statement "If you live where your summers are hot and humid or if you get rain or ice in the winter, you may want to considered growing alpine species in a controlled environment, such as an alpine house." I live at 4000' and certainly we have rain, snow, and sometimes ice. Our summers are mild. Why would alpines not survive winters with rain or ice? Thanks you. New to alpine gardening.