Forbidden subgraph problem

In extremal graph theory, the forbidden subgraph problem is the following problem: given a graph ${\displaystyle G}$, find the maximal number of edges ${\displaystyle \operatorname {ex} (n,G)}$ an ${\displaystyle n}$-vertex graph can have such that it does not have a subgraph isomorphic to ${\displaystyle G}$. In this context, ${\displaystyle G}$ is called a forbidden subgraph.

An equivalent problem is how many edges in an ${\displaystyle n}$-vertex graph guarantee that it has a subgraph isomorphic to ${\displaystyle G}$?