The instruction format of 8086 has one or more number of fields associated with it.
The first filled is called operation code field or opcode field, which indicates the type of operation.
The instruction format also contains other fields known as operand fields.
There are six general formats of instructions in 8086 instruction set. The length of an instruction may vary from one byte to six bytes.
a) One byte Instruction : This format is only one byte long and may have the implied data or register operands. The least significant 3 bits of the opcode are used for specifying the register operand, if any. Otherwise, all the eight bits form an opcode and the operands are implied.
For example :
1 1 1 1 1 0 0 0 
CLC : clear carry
This is an operation without any operand, which clear the carry flag bit.