What is another way to define the term gender role

Gender role can be defined as "Societal expectations about behavior" - this is how people see it these days. 

So, this means that for example men are expected to be strong and women protective towards children (which is not necessarily true and which can be true for the opposite gender too). 

Well gender roles are the roles we fulfill that is expected from the society towards its people. These roles are the standards or norms made by people over time and are according to culture and tradition. People try their best to fulfill their gender roles to receive affirmation and belongingness. If you cannot keep up with the role you are supposed to do, you may be condemned and discriminated. One example of discrimination might be the case of gender inequalities on preferences of LGBT communities.