String cheese refers to several different types of cheese where the manufacturing process aligns the proteins in the cheese.
When mozzarella is heated to 140 degrees, the milk proteins line up.
It is possible to peel strings or strips from the larger cheese.
In the United States, string cheese generally refers to snack-sized servings of low-moisture mozzarella.
This form of string cheese is roughly cylindrical, about 6 inches (15 cm) long and less than 1 inch (2.54 cm) in diameter.
The cheese is cut and packaged, either individually or as a package of several lengths.
The cheese used is nearly always a form of mozzarella, or a combination of mozzarella and cheddar.
This type of string cheese gets its name because it can be eaten by pulling strips of cheese from the cylinder. (source)
So can hamsters eat string cheese?
It is fine for them to nibble.
However, it isn’t nutritionally good for them and so isn’t a food that they can eat often or eat too much of as it may make them sick.