Generally, when we heat a solid substance, it melts first and becomes a liquid. If we keep on heating it, it will convert to a gaseous state. The first process is known as melting and the second one is called boiling. Sublimation is the process in which a substance, when heated, converts from a solid state to a gaseous state directly, without melting (and thus becoming a liquid). Some of the common substances that undergo sublimation include, iodine, camphor, dry ice, napthalene or mothballs, etc.
Since, heat is supplied, sublimation can be called an endothermic reaction. Sublimation takes place when the temperature and pressure are less than the triple point (the temperature and pressure at which a solid, liquid and gas coexist) of a given substance. Thus, substances can sublimate given appropriate conditions; hence sublimation is not specific to a particular substance. It is just that it can be observed at room temperature for something like camphor.
Also, note that sublimation is a physical change and not a chemical change, since no new compounds are formed.
Hope this helps.