The term "evergreen" means having foliage that persists and retains its color throughout the year, rather than changing color according to the seasons. The term is something of a misnomer, as the color in question needn't be green. For instance, Colorado blue spruce trees are evergreens, but the color they retain throughout the year is a silvery blue. There are also plants with golden foliage that qualify.
Trees and shrubs can be classified as either evergreen or deciduous. Another term that comes into play here is "conifer." Many conifer trees are evergreen, but not all, so the two words are not synonymous. The tamarack or larch tree, for example, is a conifer, but it is not an evergreen.