What is meant by "grades of steel"?

Grades of Steel is a means to identify the strength properties of the steel.

Grades of steel have absolutely nothing to do with quality, rather, is a means to identify the strength properties of the steel. For example, Grade A Galvanized steel and Grade 33 Galvalume steel have minimum yield strength of 33,000 psi. Grade E Galvanized steel and Grade 80 Galvalume steel have minimum yield strength of 80,000 psi. Grades of steel are used along with gauges and shapes of steel products to optimize performance