mass is (basically) how much matter you have there. Wood is less densely packed with matter than steel, so wood density is less (density is mass per volume).
Now weoght is a slightly different animal. Weight is the amount of force our earth pulls on the mass..The more mass the more weight, but different places on earth pull with different strength, so the same block may have the same mass, but different weight depending on its location.
(The true definition of mass is, how much it resists acceleration by a force.)
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