Why do we say that spiderwebs are "stronger than steel"?

What part of a spider web is so strong? They can easily be pulled, moved, broken so how how are they strong?
Spider webs are not stronger than steel. [2] At best, spider silk might compare to steel when it comes to tensile strength, which is the largest stress that a material can withstand before breaking. For one variety of spider silk the value of tensile strength is just above 1 GPa, a unit of measuring force per unit area. That equates to a mid-range value for steel, where strengths range from 0.2 GPa to nearly 2 GPa. [2]  Furthermore, the stiffness of silk, which is its ability to deform elastically when force is applied, is many times less than that of steel. On a per-weight basis then, silk starts to look more interesting, with the ratio of strength to density exceeding that of steel. [2]  
Spider silk is considered to be stronger than steel mainly due to its tensile strength [2]. Tensile strength is the measure of how much stress a material can withstand before breaking [2]. While tensile strength is important, there are other critical properties to consider, such as stiffness, which is the material's ability to deform elastically when force is applied [2]. On a per-weight basis, spider silk is about six times less dense than steel [2].