This is a very small (5 x 4 x 2 mm) horizontal SMD SPST pushbutton switch.
This is a surplus product. It was obtained from a surplus store, from an inventory or from any other secondary source. You can expect this product to be in good working condition, but it can show signs of being handled, shipped, repackaged etc. The supply of a surplus article can suddenly run out, or the price can change. Get it while it is available.