Does it mean the force which is used to unlock the interlocking is friction ?

Force of friction is the force that develops at the surfaces of contact of two bodies and impedes (opposes ) their relative motion. When two bodies are in contact with each other, the irregularities in the surface of one body get interlocked in the irregularities of the other surface. To move one body over the surface of the other, these interlockings have to be broken. Hence, some force has to be applied. This applied force is a measure of friction between the two surfaces in contact which acts in direction opposite to that of the applied force. 
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