I think tender annuals are ones that need to be planted in the spring after last chance of frost. Hardier annuals can be planted the previous fall and then bloom the following year. I think that's what it is at least, but I don't really grow annuals so I'm not positive.
I believe that is right - that tender annuals cannot withstand any frost. Morning glories must be one because they are the first to go here, while other annuals like cosmos or zinnias hang around until a freeze.
Welcome to the wonderful world of gardening, Terese!
People have posted while I was writing this, so I apologize if it's restating what's been said. :-)
Oh, and I consider Impatiens to be tender, but please read on for more thoughts...
I think these terms are quite subjective. For example, Thompson & Morgan (seed company) uses the terms "hardy annual" and "half hardy annual." Which, in their catalog index, a hardy annuals are described as "Plants...[which]...do not need to be raised indoors but can be sown direct into their flowering positions in the garden in spring." Half hardy annuals have the description "Sown in early spring and given protection... Most HHA's are frost-tender and must not be planted outdoors until all danger of frost has passed."
To me a tender annual (which Thompson & Morgan would consider "half hardy annuals) would be a plant that will not tolerate any frost. Usually tender annuals like warm weather, and in some cases might not withstand temperatures below 40°F. Examples I would include are moss rose (Portulaca), New Guinea Impatiens and morning glories.
I think of hardy annuals as the ones which will tolerate freezing temperatures and/or frost. I'd include pansies, snapdragons and ornamental cabbage among them.
A tender perennial usually refers to a plant that is truly perennial in climates with mild winters. In my hardiness zone, 8a, lantana, anise sage (Salvia guaranitica), and cannas usually survive our winters unless we have extreme or prolonged cold. The average minimum temperature for my zone is between 10 and 15°F, but it usually only gets that cold one night each winter - if that often.
There are so many factors that can affect a plant's hardiness too, such as stress going into cold weather (i.e. lack of water, insect invasions). And, to top it all off, many times within one person's front and backyards, microclimates will exist that may be warmer or colder than other areas. A south-facing brick wall with a sloping grade away from the house will usually create a warmer garden spot than an open area that is the lowest point in the yard.
Hope I've helped and not confused the heck out of you! A wise gardener is one who knows she/he still has much to learn. :-)
This is an example of a not-so-tender perennial...
It is a Geranium. I have no idea what variety it is. I don't normally like geraniums as they are so common, but this one was unique.
That is snow on the leaves.