The bar is a rigid straight finite object that is attached to one fixed point. The bar can be moved but the point where it is attached must stay where it is. In theory, therefore, the bar can be rotated around that fixed point in any direction. At the level of mathematics that your question suggests, the bar is movable in only one plane.
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It means turning around a fixed point or axis.
rotating on a fixed point
It is the locus of all points such that their distance from a fixed line (the directrix) is the same as their distance from a fixed point which is not on that line (the focus).
the price wont change,
It is an average rate of movement of an object (relative to some fixed point). If an object moved at this rate for one hour, it wold have travelled 10 kilometres.