Wormholes provide random and rather short lived connections between solar systems and may also lead to unmapped systems, commonly called wormhole space or W-Space. They can be found scanning down cosmic signatures with Core Scanner Probes.
A wormhole only allows a limited amount mass to transit through it during a jump, which can prevent larger ships from going through. It also has a higher total mass limit and will collapse once the total mass limit has been reached. This maximum jumpable mass as well as total mass varies by wormhole type, which means that some wormholes may let large ships, such as Battleships or Dreadnoughts, pass through them while nothing larger than frigates may pass through others.
The information window of a wormhole will provide some rough data about the wormhole, such as the nature of the system it connects to and whether the wormhole is close to a collapse due to its life time or its mass having been used up.