Semi-transparent stain is true stain; it penetrates the grain and the access is removed. Professional grade semi-transparents tains are non-film building; meaning once dry, there is no tangible layer to peel or chip off. Semi-transparent stain does not cover any cosmetic flaws; oil stains from grill, etc.
Solid stains look similar to paint but behave similar to stain. Solid stains cover all cosmetic flaws but they also cover the grain. they do not peel or chip off like paint.
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Images of solid stain: