A semi-precious stone is also known as a gem or gemstone (also a jewel, a gem, a precious stone), which is a portion of mineral, which, in refined and cut form, is used to create jewelry or other embellishments. There are also organic resources or precise rocks that are not minerals (for example jet or amber) that are also used for jewelry and would also be considered to be gemstones, as well.
In the West, precious stones are diamonds, sapphires, rubies and emeralds. All other stones are considered semi-precious stones. However, this is a commercial based classification and was a distinction that marketers created years ago which gives the false impression that precious stones are more valuable than semi-precious stones.
For example, a Tsavorite green garnet is more valuable than a mid-quality sapphire. It’s a concept from the West that often puts misconceived notions of the truth into consumers’ minds. So contextually there is a difference between semi-precious and precious but it is mostly for show and strictly from a commercial perspective.