Flatten

Flatten[list] flattens out nested lists. 

Flatten[list,n] flattens to level n. 

Flatten[list,n,h] flattens subexpressions with head h. 

Flatten[list,{{s11,s12,…},{s21,s22,…},…}] flattens list by combining all levels sij to make each level i in the result. 

Please visit the official Wolfram Language Reference for more details and examples on core symbols.