The machine cycle is the basic operation of the microprocessor to perform any activity. For each part of the instruction cycle to complete specific number of machine cycles are required.
The CPU continuously performs the machine cycle in order to execute the program instructions one by one.
The instruction cycle consist of sequence of four steps. These four CPU operations  includes Fetch , Decode , Execute and Store.
The CPU performs number of machine cycle rounds to complete fetch , decode, execute and store operations.
And therefore , In order to execute one single program instruction , the CPU might need one or more machine cycles . The number of machine cycles required depends upon the type and the CPU architecture.
For example, the both 8085 and 8086 will need different number of machine cycles to execute the same instruction.