In normal conversation the words frost and freeze are both used to indicate that it’s cold outside. Gardeners need to be aware when frost is forecast so that they can take precautions to protect tender plants. In fact there is a real difference between frost and freeze and this is important because while you can protect your plants from frost, in freezing conditions such protection is ineffective. This article which I found on the Penn State Extension website explains the technical distinction between frost and freeze.
Frost, ?killing frost,? freeze warnings, a ?killing freeze? – what is the difference? In casual conversation the terms frost and freeze are often interchangeable but there is a very real difference. Frost and freeze are two distinct phenomena. These terms take on significance when they are associated with the growing season for home gardeners.Home gardeners are just as concerned about frost and freeze damage as farmers and other growers.
According to the National Oceanic and Atmospheric Administration (NOAA), frost is the formation of thin ice crystals on the ground or other surfaces in the form of scales, needles, feathers, or fans. Frost develops under conditions similar to dew, except the temperatures of the Earth’s surface and earthbound objects falls below 32?F.
A frost advisory is issued when widespread frost formation is expected over an extensive area. Surface temperatures are usually in the mid-30?s. If a frost period is sufficiently severe to end the growing season (or delay its beginning), it is commonly referred to as a “killing frost.”
See more at Penn State Extension