| A nuclear warhead is an atomic weapon specifically designed to be used as a missile payload. The term comes from conventional munitions, where the difference needs to be made between a "dumb" bomb (one with just fuse, explosive, and stabilizing fins) that is dropped from an aircraft or fired from an artillery piece and one mounted on the business end of a missile, torpedo, or other propelled carrier. The term "warhead" is also used to discern between practice and live ammo.
The primary considerations in a nuclear warhead are yield (also referred to as throw-weight) and deployment configuration. These two aspects can be closely, but are not neccessarily, related.
Yield is how big the boom is. Tactical warheads are "relatively" small bombs with explosive equivalents of less than 100,000 tons of TNT (100 Kilotons), and are usually deployed on intermediate- or short-range (so-called "battlefield nukes") load vehicles such as the Tomahawk cruise missile or Russian Toka short-range missile. Strategic warheads have yields into the millions of pounds of TNT (Megatons) and are deployed on bomber-borne attack missiles as well as silo- and submarine-based intercontinental ballistic missiles (ICBM)such as the silo-based Russian SS-18 or the US sub-based Trident.
Deployment is how the warhead is carried by the missile. The two primary ways involve how many warheads are on the missile and how they make their final way to the target. This has little to do with the yield, but the mission. Single-warhead deployment is best when there is only one target, or precise guidance is needed. When many warheads are deployed on a single missile (called Multiple Independently-targeted Re-entry Vehicles, or MIRVs) it is ususally done to increase the chances of striking strategic targets like cities or enemy missile bases where countermeasures may destroy some warheads or simply as a force multiplier to maximize the amount of damage a single missile can do. | 
