• A deadlock occurs when a group of processes is stalled because each process is holding a resource and waiting for another process to obtain it.
• If all four of the following requirements are met at the same time, deadlock can occur.
• Exclusion from each other: There are two or more resources that cannot be shared (Only one process can use at a time)
• A process is defined by the holding of at least one resource and the waiting for further resources.
• No Preemption: A resource can only be obtained from a process if it is released by the process.
• A collection of operations is waiting for each other in a circular fashion.

Read More: How many types of fragmentation occur in Operating System?