Spawning is what a player does when they enter a rust server for the first time. Spawning also occurs after death.
When you spawn in rust your stats will be around 60 HP(?), 50 Hunger(?), 50 Hydration(?) which means that water is usually the first resource that a fresh spawn would look for.
Spawning can be abused by the usage of Sleeping Bags when raiding to give raiders an 'extra life' in case they die in the raid.