Silk has some incredible functional properties as it combines high strength and toughness. While in conversational English those properties are often considered the same, they are different for a material scientist.
Strength is the ability of a material to resist plastic deformation (i.e. not going back to the initial shape after bending). A strong material will require a lot of force to bend to a point where the material is permanently deformed. A clay pot and other related ceramic materials are examples of strong materials.
Toughness is the ability of a material to resist fracture (i.e. breaking). A tough material will both require a lot of energy to bend, but can also endure a lot of deformation before it breaks (this property is called ductility).
Many metals, like steel, because they are tough because they are strong and also very ductile, they are able to lengthen significantly before breaking. You can get a better idea of each these properties by studying a stress-strain curve for a given material. A link is provided for you to get some more information on these:
strain and stress.
Now, silk is incredible because it has incredible strength and toughness. It is almost 10x stronger and 100x tougher (per kg) than bone. These properties are incredibly impressive and have made for both innovative armor choices (Mongolian silk armor) and funny movie scenes (Get Smart). Silk fibers, in addition to being mechanically impressive, has a very smooth fibrous structure that makes for good texture and a pleasurable wearing experience. Together, these properties begin to explain the global appeal of the fabric.
Below are links to a peer-reviewed publication and a college-level student report on the mechanical properties of spider silk. If you want to learn more, I would recommend you search up the publications that each of the linked articles cite. This should help provide some additional information.
Peer reviewed paper on silk properties.
MIT student report.