Even though the instructions can be written in hexadecimal code, it's still difficult to understand a program written in hexadecimal numbers. So, each manufacturer of a microprocessor has devised a symbolic code for each instruction, called a 'mnemonic'. (In Greek, 'mnemonic' = mindful, i.e. memory aid). The mnemonic for a particular instruction consists of letters that suggest the operation to be performed by that instruction.

For example, as u've said 'MOV' command, say --
MOV A , B
Then it's hexcode is : 78(H)
That's in binary : 0111 1000
So, if u're dealing with 8085 simulator, then 78(H) command's mnemonic is 'MOV A,B' [that is the processor then realizes to move the 8-bit data from register-B to register-A.]

I've told u the example in case of 8085 microprocessor, coz we've done lab-experiments based on it so far.

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