A "semi-desert" is determined by both climate and geographical conditions. It is a hot and arid expansive area and resembles a real desert except that it sustains a vigorous ecosystem of plants and animals adapted to survive and even thrive under such extreme conditions. It usually borders grasslands,woodlands or mountains, the latter often obstructing potential rainclouds from coming by their sheer presence. Although is has very low annual rainfall, its precipitation is higher that that of a true desert. Some examples of semi-desertic terrain would be the scrubland often depicted in American Westerns or the high plateau of Mongolia.
The word "vegetation" refers to any and all plants naturally found in such an area, including cacti, tumbleweed, and desert flowers. Another word often used is 'flora.'
A "semi-desert" is opposed to a "hot desert" by terminology. The Sahara Desert or the Gobi Desert are two examples of the latter.