150g or 180g refers to the gram weight of each individual vinyl record.  Generally the heavier the record, the better quality it is considered to be.  Standard weight varies from manufacturer to manufacturer. Typically anything above 125g is considered to be "audiophile" grade. At Train Records our standard weight is one of the heaviest at 150g.  Although the argument continues after decades about whether or not heavier records sound better. There is no debate that it makes the product more durable against scratching and warping. In addition, it makes the record more desirable and is an extra selling feature.