A drone swarm is a group of drones that coordinate with each other in the air to do one job. Each drone decides part of the job by itself, so the group needs no person flying each drone. The same product group includes high-altitude aircraft that stay in the air for days.
Ten drones flown by ten operators are not a swarm. In a swarm, one operator gives one instruction, such as "survey this field", and the drones divide the job among themselves. To do this, they exchange data over a mesh network. In a mesh, each radio passes messages on for the others, so the group can work with no mobile network. Each drone shares its position and what it sees. Drone autonomy software on each drone uses this to share out the work and to keep the drones from hitting each other.
Consider a sugar cooperative in Kolhapur that wants to survey 800 acres of sugarcane fields to find patches that are not growing well. One drone would need several battery changes and many hours. Instead, ten drones take off together. Each takes a strip of about 80 acres and flies it, so all finish in about the time one drone needs for a single strip. If one drone's battery runs low early, the nearest drones divide its unfinished strip between them. A single drone could not do that, because it would have to land.
A swarm is the highest of the levels of autonomy. The operator at the ground control station gives the job to the whole group, not to each drone. Radios for this work are described under mesh and tactical radios. Armies are also buying swarms that find targets and coordinate on their own.