A fit in which the shaft is always smaller than the hole, so the parts assemble by hand.
Clearance fits are the default wherever a part must move or be disassembled. Their weakness is location accuracy: a clearance fit locates only as well as the clearance allows.
H7/h6 is the special case that assembles by hand with zero minimum clearance — the best location a clearance fit can give, and the most-used fit in general engineering.
Specifying a clearance fit where accurate location is needed, then adding a dowel pin to fix it — when the fit should have been tighter in the first place.
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